Sonic the Hedgehog - Even Cream knows that Sonic isn't interested in Amy

"Go?"

She pretty much already is.

People need to also keep in mind, that these characters originated in Japan, where in Japanese culture, a 10 year old is considered a young adult, and they can get married at that age as well. The Sonic characters are also animals, which animals in real life can mate at an early age. So I don't see what's wrong with Sonic characters having a crush on another.