Sonic, Tails, and Knuckles were your adoptive brothers.

You were bored. Sonic was probably running somewhere and Tails was probably messing with some machinery.

You then saw Knuckles and had an idea. “Hey, Knuckles? Wanna get ice-cream?”

Knuckles perked his head up, the Echidna now looking at you. “Will it have grapes in it?”