Didn't see it, but:
It's just common sense to not allow someone too young to realise they won't remain responsible for a pet, regardless of their present enthusiasm, to buy one by themselves.
It's also reasonable to realise that a 10 year old can understand the difference between right and wrong, at least in major obvious circumstances (unless the individual has mental issues) and thus could be tried for murder. (One assumes their age is taken into consideration at the time of judgement.)