I would add, "...while yelling loudly and repeatedly that I was breaking into the car to save the child."

What if you see the person whose car it is, politely ask them to get the child out of their car, then say "if you don't get the child out, I'll break into the car to get them out, and that's legal" if they don't comply? Would that be considered an illegal threat?

In France, they also invite you to notify the bystanders of what you are about to do (i.e. saving someone from cooking in the car, and not just a car thief).

It irks me that the quoted legislature doesn't mention a reasonable expectation of harm, and seems to disregard the possibility of having the AC running/a sunroof open/a non-significant amount of time (or even distance) that the driver is away from the vehicle, it only quantifies being "unattended" as the criterion on which to base your actions.

@Someone: Going by the answerer's mention of a reasonable belief of imminent danger; it depends on the response you get. If they disregard your request and you still genuinely believe the child/animal to be in danger; then your reasonable belief still stands. If they acknowledge and/or provide a reasonable response (e.g. short time away, AC running, ...) then your reasonable belief of imminent danger ends then and there.

@Flater, Here in Italy leaving a child unattended, whether in a car or anywhere else, could be a penal crime in itself "abbandono di minore" ("under-age person abandonment"). The discriminant for the crime is the age of the child and their state of helplessness in the environment where they are left (a 12y teenager that can operate the air-con/get out of the car is different than a 5y child strapped on a seat). If the person is helpless and the caregiver leaves them even for a short time, it's a crime (more or less). This is true also for adults: a caregiver for a disabled person, for example.

@LorenzoDonatisupportUkraine: You mention discriminants in your own case, e.g. the ability to operate an AC. That entails that an AC is regarded as a solution to the problem of being locked in a car in hot weather, at which point already having the AC on (for someone who cannot turn it on themselves) must logically already be a solution to the problem of being left in a car in hot weather as well. It's important to relate things only when they are related. Abandonment is not the same issue as being left in a car in hot weather (as this is still a problem even if the guardian is nearby).

@Flater I said "operate". The point is agency. The fact that the person is helpless is fundamental. The problem is not the fact that at a given point in time the conditions are considered safe. The problem is that without agency the conditions could change and the child could do nothing about it. In Italy the crime of abandonment is regulated by art.591c.p.. ...

@Flater ... As Wikipedia points out at the end: there are some interpretative difficulties. In particular (translation by me) "The concept of abandonment [...] is not explicitly defined in terms of intent, timing or context. Therefore, during the years, there have been debates and sentences which dictated some boundaries to that notion." ...

@Flater ... and at the end "If the meaning [of abandonment] is the ability of the child to defend himself from [...] dangers, like hunger, hypothermia, [...], the judge must carry out a difficult task of assessment of the environment and the maturity of the minor"

@LorenzoDonatisupportUkraine: Just as a baseline, a person could leave their child in a car in hot weather with no AC running, stand next to the car, and refuse to acknowledge the dangers of doing this nor change anything about the situation. This is not abandonment, in the sense that the person is present; but it is neglectfully endangering the child (abandonment is a form of neglect but not all neglect entails abandonment). [..]

@LorenzoDonatisupportUkraine: [..] In this situation, it very much matter whether there is no AC, or whether the AC is running and has been set to room temperature (no overheating, no hypothermia). The issue at hand is one of the child's safety, particularly involving a car in hot weather, and the fact whether the AC is running (in a way that it both prevents overheating and does not risk hypothermia either) is a concrete solution to said problem. The core issue here is the fact that were a problem to present itself, the child cannot fix it themselves. However, [..]

@LorenzoDonatisupportUkraine [..] However, abandonment is not the core issue here, as a parent could be present yet still be unwilling to fix the problems for the child. Therefore, the core issue is not abandonment, but reckless endangerment. Abandonment is a form of reckless endangerment, but not all reckless endangerment is inherently abandonment.

@Flater That's not the situation we are discussing. To be clear, my objection to your original comment was that "imminent danger" is not relevant here in Italy if the minor has been left alone (albeit safe). Here is an article of a specialized site (in Italian) describing a case where our supreme court for criminal cases ruled against a mom leaving a 5y old in a car.

@LorenzoDonatisupportUkraine: "my objection to your original comment was that "imminent danger" is not relevant here in Italy if the minor has been left alone" I return the response: that is not the focal point of the discussion. We're not talking about abandonment, we're talking about reckless endangerment (i.e. the harm that could befall this child). Abandonment is a form of reckless endangerment, but abandonment does not fully comprise the entire concept of reckless endangerment, since you can recklessly endanger a child while still being present.

@Flater IANAL, so sorry if I don't know USA legal terms with their exact meaning. I repeat, in Italy, there is a specific article (which I cited in a previous comment) of criminal code that comprises the situation the OP has described. I wasn't trying to debate about the finesses of legal jargon. I just wanted to point out that in other countries the approach of the legislator AND the judges is different, in relation of whether or not there is "imminent danger".

@LorenzoDonatisupportUkraine: The question centers on the dangers of being in a car in hot weather, implicitly due to the dangers to one's health that can happen in such a situation. For the question in focus, this is assumed to be a fixed truth (and I'm not saying that it's not true). The legal article you refer to centers on abandonment inherently being defined as endangerment, which I personally agree with; but it does not provide an answer on how to handle cases of endangerment where there is no abandonment.

@Flater You misconstrue the Italian law there: under that law, if you leave a child under a certain aige in the car, no matter the weather or conditions like time or running of an AC, the law says that it is endangered and you can (and might have to) break the car to get the child out.

@Flater that page on the NHTSA site says "Never leave a child in a vehicle unattended — even if the windows are partially open or the engine is running, and the air conditioning is on."

@Trish ^^^^^^^^

@Someone: The NHTSA is not a legal body and does not prescribe legislature. There is also nothing stopping anyone from giving any advice that is more restrictive than what is legally prescribed. The law should not be confused with advice given by a third party or what a person considers common sense. These three things can vary wildly.

@Someone Under the Oregon law cited here, you couldn’t just make this a pretext for “reckless, wanton or intentional misconduct.” If the owner of the vehicle were right there, and could have let the infant or pet out, you might also have difficulty convincing the law that you used “no more force than is necessary.” You also must reasonably believe the child or animal to be “is in imminent danger,” and must call 9-1-1 as soon as you can. This probably means that it wouldn’t be deemed reasonable to break into their car while they were right there.

If they are right there but are not doing anything to help the child, wouldn't the child be in imminent danger just as if nobody was there?