I suppose it depends how old the kids are?
We did Y recently, via FRA with Lufthansa and it was "fine". Of course, W or J would have been comfier for the adults, but my 4 kids (6-11), had plenty of comfort and slept as well as could be expected, I don't think the cabin would have made a huge difference to the kids. (In fact, I think the novelty of seat positions, storage nooks and the extra space of a business "suite" and not being cuddled up to dad and mum may have hindered the kids.
I should add that for SIN-FRA we got seats in the mini cabin (4 rows of 10) on the 747, so the environment was nice.