you hurt Long, prepare to get hurt. Being a kid is no excuse.
If it's confirmed that the grandpa edited their memories (the other girl did remember they were at the reservoir, but didn't remember more, suggesting a "situational" or "time related" editing, while Long and Huadai didn't seem to remember each other at all nor the other kids, suggesting a more deep editing ) why he did trust a stranger with these memories, but not his future disciple and his own granddaughter (costructing an incident that made her parents and her grandpa completly alienated to each other ). However there is still the entire "scar" issue to explore.
Also as it seems it was Huadai to sort of summoned Long, and that in the flashback she seemed to know at least partially her origin, while not after. Wonder if also that memory was affected by the alteraton