Playing in the nest boxes

[HarmonyHillHomestead]

I have four almost 6 week old Buff Orpingtons who have been in the coop for almost a week now. They sleep on the roost like good little girls, but they want to spend all day napping or playing (and pooping!) in the nest boxes. If I go out they all jump down and want to play, but as soon as I walk away they are back in the nest box. I dont want them to get in this habit... but how do I stop them?

 

[sourland]

Block off the nest boxes until they are about to start laying.