Slow & steady wins the race. Also - become known at the school(s). Teachers LOVE when Dads get involved. Volunteer to help with any/all activities, volunteer to chaperone field trips, offer to help organize field days, etc... Get to know the office staff! Get involved with extracurriculars (and yes, Dads can get involved in girl scouts, too - you may need to become certified as a leader for certain activities). Go to all appointments possible. It all provides the opportunity for extra time but also builds relationships with adults who can/will vouch for you if the ex goes off the rails. Even more importantly, it shows the kids that you are fully invested in them. Hopefully Mom doesn't try to say otherwise, but nothing overrides experience in your children's minds. They will know the truth. And, perhaps most importantly, you are also building towards the relationship you want to have with your kids as adults. When they are grown and can vote with their feet? They will ideally walk between you and their Mom, equally. But if they don't? You want them walking with you.