I have it in my parent policy handbook that flip flops are not allowed, that all footwear must be secured to the foot. I just sent out an email reminder to parents about a week ago reminding them of the summer weather requirements - hat, sunblock, footwear, etc.

I had a 6 year old boy last sumer that was sent one day, despite my policy, in flip flops and I spent half the day putting his shoes back on because he would climb up on the play structure or something and he shoes would fall off. I just told the mom straight out at pick up time that he couldn't wear them to daycare and told her why (nicely, of course).

I wouldn't even allow the flip flops with the back elastics, those don't stay on very good either. I tell parents that the shoes must be good for running, jumping and playing in all day.