Armorplate, what good advice, to stop and hug! Thats replacing a bad habit with a good one.
I have the same thing, i can be sooo short-tempered with children. I get that it is how THEY were raised, too, but still it is scary to have those feelings.
I would also recommend taking breaks when possible. Nap when they do, or call in a babysitter for a short bit. When i was "helping" my parents babysit the nephew when his other grandparents passed, angelic as he was (and he truly was!), i couldnt WAIT to fly out the door!