Please can people give me some idea whether this is typical behaviour for a child of the specified age. Thanks.

A ten or eleven year old kissing a child of four on the lips in a prolonged way when adults leave the room. They are of the opposite sex.

An eight or nine year old using a child of two for masturbation when the younger child is asleep. They are the same sex.

An eight year old knowing how to reach orgasm.

I'd really appreciate thoughts on this because what I've read about ages and sexualised behaviour seems unclear.