Child custody cases sometimes involve a parent who isn't really present in the child's life. When that parent decides that they want to come back into the kid's life, the court will likely allow that to happen unless there is a reason, such as abuse, to refuse. This puts pressure on the parent who has been there, as well as the child.
Both parents will have to work together to ensure that they are handling the situation in the manner that is in the child's best interests. The parent who is coming back might be excited and ready to push things forward quickly; however, this might not be what needs to happen.
It might be a good idea to talk to the children and see how they feel about the situation. It is possible that they will be apprehensive to allow the returning parent back in. This is understandable, but the custodial parent can't keep the kids from that parent if the court says the parent has rights to see the children. In this case, the custodial parent might have to discuss the requirements with the kids and let them know that they do have to see them.
Throughout the reintegration process, both parents should talk to the children to see how they are faring. It might help if this is a joint meeting that includes all kids and both parents, so everyone is on the same page. Don't be surprised if the kids are still rather shy. They might want to speak only to the parent who has been around consistently. That parent might have to help them work through their emotions.
The returning parent should understand how difficult this is for the children. It is going to take time to rebuild that trust. Always showing up for parenting time and communicating often with the children might help in these cases. Ultimately, both parents should do what is in the children's best interests, which includes following the court orders for visitation, parenting time and support.