They are overtired, plus having a hard time winding down.
With my kids, I actually EXPLAIN to them... that when they get like this, and are fussy and getting on each others nerves.... it is when they are OVER-tired... I explain their "symptoms" and how when they DO get enough sleep and rest... they feel much better. And they agree. So instead of fighting with them about "go to sleep!" I just explain to them, that all this restlessness and irksome antics, is just because they are over-tired. So.. that means... they and their body need rest and sleep.
Otherwise, it dominoes all week. And they won't have a fun weekend.
And I also make the house all dark (except for 1 lamp on)... like 1 hour before bed. To get them keyed down. And prepped, for bed... per the environment.
My kids are 6 and 9.