1 in 100k cancers also disappear spontaneously, should I wait and see for my kid and not treat them?

As a parent, a cancer survivor, and the child of a high anxiety parent, Yes, yes you should wait and see. Every doctor's visit is a chance to catch something worse.

That said, if you're a chill parent reading this, you should probably be more proactive about it. There is a middle ground, overreacting is usually worse than under reacting, but it is important that you react.