For tonight, just allow him to be "cool dad" don't let it affect you.
Through out history it's never been the "cool" parent or teacher that made the greatest impact on the child/students life. It was the one who gave discipline and structure who made the impact and walked away with the respect. So continue to be you, when they are with you.
Your H is probably giving them want they want to keep them happy, busy and because he may not know what else to do, that's why I say for now just keep a PMA at the dinner, get your thoughts together on the matter and proceed how you think is best in a few days. Maybe you'll decide that you would like to sit down w/ your H in the next week or so and discuss the kids and things to help w/ their transition during this process? And let him know you'd like to keep certain structure in place while they are with him and see what he's open to doing?
me: 30 H:30 tgthr:7 m:4 no kids 5 counseling sessions initiated by H as a LR: Oct 2012 long distance marriage b/c of work since Nov 2012 official BD: July 2013 nothing filed 1/1/14 I dropped the rope