I use a tripod with 4x5 and 6x6 but never with 35mm.
I just bought a Mamiya 7 II and would like to use it mainly hand held. We'll see.
With portraits on 6x6 and 35mm it is almost always better with a tripod because at the moment of exposure the mirror goes up and you don't see the expression, blinking etc. However when shooting lifestyle kid stuff a tripod might get in the way.