Laughing, You did the right thing by asking your friend to accompany you to drop the children off. I imagine he was quite surprised to see that you had done that. From last night forward, you will need to have another party present when you do this. You do not want to give him anything to use against you. The witness will put his fire out for he shall not be able to push your buttons in his/her presence.
As for your children, I'm counting on your daughter giving them the blues up front and center. She's a smart cookie and will give it to her father in a heartbeat and not think anything of it. Now your son, he's at the impressionable age and promises of this or that will reel him in. Unfortunately, the reeling will take place for a while, but the actual payment on those promises may not over occur. Your son will see the light in due time. Do not ever worry about that. These two so call grown ups have a lot of growing to do in the months ahead as your children could teach them both a few things.
Laughing, you are their lighthouse in the storm and your children will return to you for stability and love. Never doubt that. I'm hoping that the current storm will die down and things will get back to normal after a while. Your xh knew that this was the one area that was a bone of contention for you, so he went after you full force. When he discovers that you are enjoying your "free" time and doing things to move forward, I promise you, the visitation will go by the wayside.
Hang in there.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.