We had a nice cruise on the L, but my 13 yr old was a bit disappointed--and we are spoiled by
DCL's movie theater. We were expected a DreamWorks experience. L does have many photo ops with DreamWorks characters--Shrek, Fiona, Panda, etc---but don't expect to see those movies in a theater experience on board. Puss/boats and another movie were on the TV, but L doesn't have a movie theater. They showed 1 3D movie in the auditorium on a 4 day cruise, and 1 PG movie late at night by the pool. During the day, the pool screen showed poker, tennis, and other sports--no movies (at least when I looked--which was often). I even asked at guest services if I was missing something.
Unless super adventurous, a 7 yr old is unlikely to do flowrider (I think that age might be able to knee board--but maybe too young), certainly not the climbing wall. So, that leaves putt-putt, kids club, and some DreamWorks stuff. So, even though L is "bigger" that might not be better for a 7 yr old. My 13 yr old was too timid to do flowrider or climbing wall. We did enjoy the ice show.
At 5-9 yrs old, my kids loved RCCL kids clubs (more so than DCL kids clubs on the Dream). They really preferred the smaller ships for my personal attention vs. the larger ships with many more kids.
Brilliance, while not having the DreamWorks stuff, has a small movie theater--which tends to show the same movie all day--so on a 4-5 days cruise, probably at least 1-2 movies might be G rated.
If your child will go into a kids club, then I think the Brilliance would be fine, as the more active stuff is too old for her on the L.
Don't know how much that helps--but the lack of movies really shocked us, esp. given the hype about DreamWorks--sorta weird.