I would discuss it with your mate. He may be ok with it, but you will never know until you ask. Here is a question for you, If he says no, are you going to do it anyway? You have to be honest with yourself and your new beau. Don't make it an issue when it comes to the kids, just tell them they are spending the day with daddy and you won't be able to come. Its hard at first, but I promise it gets easier, the kids come to accept it and quit asking you to come with.