I would have to say I wouldnt be so worried at that age of my boys going into a bathroom alone. I would warn them they had 4 mins, and if they werent out I would be coming in, and wouldnt it be embarrassing to have your mom come in?!?
I had my friends 9 yr old son with me, and he went into the bathroom alone to change after swimming. I would have to say this was my worst nightmare. There were two exits, and even though we specifically discussed where he should come out, and not to leave guess what he did? He went out the opposite door, and wandered off thinking he could find me! He is a very smart, and wise kid, but this time it just escaped him. My first instinct was to get a CM, and I kept calling for him. We found him a few hundred yards away crying, and with a group of STANGERS!! trying to help him! All those things we have told him NEVER to do, he did. So do go to a one exit bathroom, and give them a few minutes before going in. If all else fails grab some man coming out and ask him if he would call to your sons that their mom is waiting and they had better hurry. Or you can always grab a CM as ask him to check on them. I love the two way radio idea.