Percy Jackson is a son of Loki and Sally's sister Sarah, Loki can't stay for obvious reasons and Sarah died in a car crash. Percy goes to live with his Aunt Sally who adopts him at age 4 along with her lover Poseidon also adopts him for he senses he is also a demigod and a possible chance for him to be the child of the prophecy anyways.
Age 8 Percy finds out he is a demigod and goes to Camp Half-Blood
Age 12 defeats Kronos
Age 13 defeats Gaea
Ages 9 to current (13) finds out his magic powers and some say he should be child of Athena for he reads for a long time.
I know the ages are all wrong but I like this Percy Jackson meeting the Avengers at a young age. Takes place during/after Avengers movie and Before/During/After Age of Ultron