I dont have kids so I don't know anything authoritively. I only know what things were like for ME as a kid.
All kids are different, and some of them will love Europe and some will not care so much.
The main thing to remember, as far as I am concerned, is that a ship with a solid kids program will mean they have the option of staying on the ship and playing and it won't spoil YOUR trip - just "if" they happen not to care about the sights.
That is one of the advantages of a cruise ship.
One the other hand - of you WANT THEM to see Europe with no other excuse or other option than to stay with you (perfectly reasonable outlook) then you can consider a ship without much of a kids program, and then they won't have any choice except to go on the tours with you.