Please note that currently RCI are only allowing fully vaccinated travellers on board, and that includes children, so I'd be reluctant to book anything just yet unless you were guaranteed to be able to get your money back easily.
Otherwise, I love an RCI cruise (done 4 now), though only as a couple.
There are teen clubs and hangouts so if you're going in the school holidays there will likely be similar aged teens to hang out with.
Otherwise in terms of things to do, there's loads, especially on some of the bigger ships: mini golf, sports court, surfing simulator, pools, gym, climbing wall, ice rink (which often gets converted in to a laser tag venue), arcade, etc.
One thing to be aware of is that the internet packages are really expensive and often not very good, so we don't bother. We just connect up to local data in ports, or grab some free wifi somewhere (follow the crew - they always know where the free wifi is!)
If you have teenagers that are permanently connected to their phones this is either a recipe for disaster, or a golden opportunity to be able to spend some time together!
If you are going in the school holidays it is expensive! While on board we priced up a cruise for my SIL and her family (2 adults + 2 small kids). A 2 week Med cruise in July was over £7k. In an inside cabin. 
The food is fantastic. You have lots of options included within the price plus some speciality restaurants that you can pay extra for (there are often deals to be had). Really though, the main dining room experience is great. We had a drinks package last time and it took our waiter all of 2 days to know that I liked a glass of white with my meal and it was waiting for me at my table every night after that.
The buffet is great too - normally a variation on what is being served in the MDR, but in a more casual environment.
They do have dress codes on RCI but they're not strictly enforced like some other lines.
If you do book (or even before you do), head on over to the forums on Cruise Critic's web pages. The knowledge over there is great and there is normally a page set up for your particular cruise so you can start getting ideas together or group excursions booked. We had a fabulous trip booked in Iceland through an independent company, which was organised by someone on our roll call.
We love a cruise - it is the type of holiday you make it. A lot of people will call it "Butlins at sea" but we love the relaxation. You can get involved in as many or as few activities as you like and the cruise planner gives you a heads up on where to be or where not to be, depending on your decision!
I can't wait to get back on a ship!