Divorce can be difficult on your family but it is extremely important not to find yourself hurting your children in the process. They are the most important to protect during this time of transition and there are a few things to remind yourself of every time you are interacting with them.
First, make sure you understand the terms of your custody agreement. If you want to make changes be sure to go through the proper channels to make those changes. If you feel like your custody agreement isn't being honored or you'd like to make changes, contact your divorce attorney for more information.
Second, don't try and force them to take sides between you and your ex, no matter what your situation is. They are too young to be handling anything of this emotional magnitude and as their parent it is your place to protect them from this strife as much as possible. To them, they still have two parents and might want to keep it that way no matter what you want. Allow them the space to express what they want without trying to influence them.
Another very important piece of advice to follow, do not bad mouth your ex-partner in front of your children. Not only can this be psychologically damaging to them, but it can also cause rifts between you and them or your spouse and them. This action can come back to hurt you in future custody proceedings.
Finally, try to not let the stress of the divorce and its toll on you affect your relationship with your children. As difficult as it may be right now, protecting your relationship with your children is paramount and your children can be a source of comfort and love.