Please be gentle with yourself here and remember that a child cannot consent to any form of sexual activity, period.
Sexual abuse does not have to involve penetration, force, pain, or even touching. Anytime someone engages in sexual behavior (looking, showing, or touching) with a child to meet their own interests or sexual needs, it is sexual abuse.
All sexual engagement between an adult and a child is sexual abuse. Sexual engagement between children can also be sexual abuse when there is a significant age difference (often defined as 3 or more years) between the children or if the children are very different developmentally or size-wise.