Right, Why is it a chumra to have a newborn baby sleep in the succa? The baby is not chayav, neither is the parent obligated.
ETA
Unless you say that the baby is indeed mekayem mitzvos....R' Moshe holds like this. (cant remember where)Young children who keep mitzvos are actually fully performing the mitzva. -Like R chaim soloveitchik by hilchos korbon pesach (koton sehigdil bein shnei pesochim is pottur from pesach sheini, because he was yotzeh...)