You should involve the court to get a permit to see your kids. However, this will also depend on the first cause of the separation and why he had to get the primary custody. If you still have the right to see them, the court will rule on your favor.
Try to contact your children and talk to them until your scheduled visits. if the visits are scheduled, its for a reason and if he really wont let you see the otherwise just call your children and talk to them. waiting for the scheduled visit would make seeing your kids a lot more better and you can cherish the moments with them.