Lacking any exemptions, the normal rules on alignment would apply.
All creatures have an alignment and alignment determines the effectiveness of some spells and magic items. (PFSRD, "Alignment")
It goes on to say this.
Animals and other creatures incapable of moral action are neutral. (PFSRD, "Alignment")
So creatures incapable of moral action are neutral (although some monster entries are mindless yet evil, which I assume is an attempt to indicate the moral considerations of the creatures creating them, rather than the mindless creature itself). However, humanoids are nearly universally considered capable of moral considerations and have alignments. Anything that is a playable character can also have various alignments unless noted in the 'race' entry.
The 'Young' template, the only metric to judge children vs adults in pathfinder, does not specify that the target must be Neutral, or otherwise indicate that the Pathfinder roleplaying game system considers children or adolescents 'incapable of moral action'. The GM can decide that specific children or Young monsters have a different alignment than the norm for that monster or race (or class) in the same way they can alter alignment for any individual npc or monster the party might come across, or in the same way they can alter the alignment of any demographic (poor, mercantile, slaves, wealthy, desperate refugees) that might live differently than the 'normal' monster or humanoid of that type and therefore have an altered alignment. This is not spelled out in the rules, but can be inferred from the general Alignment and Gamemastery sections of the core rulebook.