From Wikipedia

May "Mayday" Parker is the child of Peter and Mary Jane Parker in a future, alternate universe continuity. In the MC2 continuity, they were reunited with their baby daughter by Kaine, who found the child living with Alison Mongraine, the con artist who had kidnapped the baby on instruction from the Green Goblin. After they were reunited, Peter lost a leg during the horrific final conflict with the Green Goblin. After the battle Peter was offered a bionic replacement from Mr. Fantastic and, considering it a wake-up call, decided to retire and focus on being a husband and father (the battle is glimpsed in Spider Girl #7, and fully explained in Spider Girl #49). For years, they chose to keep their past from Mayday and hoped that she wouldn't develop powers of her own.