@Joe They're all basically the same as far as kid appropriateness. R2-D2 is already fully constructed and employed in the Naboo Royal fleet in Phantom Menace. When Anakin is freed and leaves with the jedi, he leaves C3PO behind, who is built except for outer coverings.

@KarlBielefeldt Thanks! I must have had R2-D2 and C3P0 backwards.