Sonic and tails in this AU are 6 years apart (sonic was 10 years old, while tails at the time was 4 years old when they met)
Sonic in this AU lived on his own along side some critters. Because of this he never knew how to talk properly. In a nearby village however he would observe the locals and their families. One of them was a mother rabbit taking care of her newborn child.
After Sonic found tails one rainy day, he took him in and mimicked what the mother did with her child (he washed him, feed him, and even gave tails his only shirt just so he can be warm)