First of all, niether of them have a confirmed age. They are just referred to as a kid. They could be teenagers for all we know (but they certainly aren't adults.) You can interpret them as any child-teen age you want during the time period of the game.
Second of all, do kids...not have crushes on each other? Do kids...not grow up and fall in love sometimes? Because I know plenty of people who are now married to their childhood crush.
Third of all, they aren't gonna stay kids forever anyways. They'd grow up at some point.
Honestly, I don't see why youre even bothering commenting on things you don't like. Find something better to do.