If the danger is immediate, call 911. If the danger is not immediate or serious, talk to the other parent about your concerns. Do not make the issue personal; put the focus on keeping your child safe. Think about what the other parent could do to make you more comfortable with the situation, and come up with a plan together.
If the other parent does not listen to your concerns, and the danger is immediate; call law enforcement. If the danger is not immediate, a protective order may be appropriate. Follow the protective order with a request that the court modify your visitation order. If you think that the child is in serious and immediate danger, contact 911(in the case of an emergency) and/or Child Protective Services at 1 (800)-252-5400 if you believe the child is being abused or neglected.