What has worked best for my family is when the other parishioners step in.
Some days my kids can't sit together w/o distracting each other; but when they go sit with older couples, they are angels. (Usually).
Also, often parishioners magically show up mid-tantrum with a bauble, or paper with crayons. Often, all it takes is a little distraction from the tantrum to head it off.
I can not tell you all how grateful I am for the wise parishioners who have all: been there; done that.