Seth MacFarlane just made a young fan's dream come true ... and the kid's whole family joined in on the Hollywood adventure.
Thanks to Seth and the Kids Wish Network ... Chance Yon -- who has cerebral palsy and suffers from ROHHAD -- got to spend the day with his hero at the animation studios of "Family Guy" in L.A.
We're told Chance and his family were flown out Tuesday and greeted with balloons, welcome signs and MacFarlane himself. They had lunch, and then Seth drew and signed sketches for Chance and even voiced some of his favorite characters for him. Mila Kunis and Seth Green -- voices of Meg and Chris -- also chatted with Chance on the phone.