I was about to say that they might be coming down with a flu or something. Mine get like that just before they're sick. Especially if they're a bit tired & run down at the moment.

Kindy here is only 2 days a week, but if it's more, maybe let them have a day off to see how they go & let them have some quiet time. I know my little ones need it more than my big ones, & Sunday is always a 7.30 bed time, or earlier after a big weekend, just because they are so worn out. It'll usually take the best part of the school week to get over it.

ETA - if you are going to let them have some time off, make a point of it being because they're sick/tired & that they can only have time off for those reasons. I'm lucky that mine are the opposite Its a fight to make them stay home when they're sick!