Took the Pont Aven during the summer.
If you bring young children, I would definitely recommend night sailings so you all can sleep some of the journey away.
Couldn't get a four-berth (My wife, myself and three children).
Took 2 x 2 berth cabins. Cabins were quite small but sufficient for a night's sleep and included a shower. Wouldn't want to be planning on spending too much time in them otherwise though.
Food was pretty much what you'd expect, pricy and pretty bland. I'd advise brining some snacks on board for the kids.
Otherwise, crossing was excellent. Boat is very spacious, plenty of room to walk around etc. Service was good.
Personally, I think it's a better option that flying/car rental given that with a roof box, you can bring practically everything you or the children will need during your holiday.