The almost one year old was hard, as she crawled and so her clothes got very dirty, since they're all fleecy stuff. Also she liked to eat dirt and drank formula and ate baby food. Heavy to carry, hard to heat and messy to eat.
Now she's heading towards 1.5 it will be easier, she can walk around(not hike) and eats regular food with reasonable success.
I had that pack just absolutely crammed, I was jamming stuff in as hard as I could and still ran out of space. The weight was fine, at just under 50 lbs with about a gallon of water, the suspension was up to it(and it was a short hike). I bought this Mountainsmith pack used a few years ago, specifically for use one family hiking trips, but that was with one kid. It's not crazy heavy at about 1300g without the lid, and I would guess about 70l.
With two though, including a baby, it's a bit more stuff. The second trip I used my old Lowe Alpine Alpamayo 90 behemoth just so it would fit easier, which it did, in fact there was a fair bit of empty volume. That beast weighs about twice as much as the Mountainsmith though.
Both of these trips were with very minimal gear since it was just for one night in fairly dry weather. On slightly longer trips or in more inclement weather I would have to bring more, and the youngest is up to 25lbs buck naked, so the child carrier is going to be heavy just with her in it, not much weight left for gear.