What if I don't tell my ex that our son got a black eye at school
Are you on speaking terms with your ex?
We don't have a good relationship.
You should inform the other parent of your child's injuries. She could accuse you of beating the kid and try to take full custody.
Never know maybe I will take my son for a week.
You have to be careful here. Document your conversations. You should also consult a family counselor or even lawyer if necessary; if you think she's unstable or combative, you have to protect yourself.