My DD's hardly ever sit still at our meetings either and there are plenty of other kids that don't.....thats why we have a mother's & baby room to escape to.
Honestly if your pil feel under stresssed by taking him to the meeting, everybody else there will probably love having some kids to fuss over and won't mind in the slightest.
I have to 2 dd's to occupy at meetings 3 times a week! colouring books are wonderful!