It is very difficult for any person to opine as to what is best for a particular family or child within that family.
I remember both myself and my children getting dirty looks when we boarded the Radisson Diamond back in 2003 (I think) which would put my daughter at age 4 and my son at 7. They had a blast and by the second week it was almost embarrassing how many people came up to us and complimented our children admitting their initial prejudice.
My kids have also enjoyed the Regent Mariner, Regent Navigator, I think 7 Celebrity cruises, Cunard, NCL, Royal Caribbean, etc....even the Big Red Boat II. Now which do they like the best? Which was the last cruise????
But for my children, even with a limited children's program, I do not believe Seabourn is a good fit for them. Seabourn may not like me saying that, but I say what I think.
Now, I have seen a few children on Seabourn and I have reports of very happy children and teens. And, to be sure, there have been a complaint or two, but the vast majority of folks have either said nothing or said positive things.
Soooo, for some families Seabourn is obviously a great fit. For others possibly not. But what someone else perceives may or may not be right without knowing the family and kids...