I am only 15 so this review will be from my perspective and this may or may not help you when deciding to book a cruise if you have teenage children.
I had been on two cruises before this one however they were both Caribbean. I was slightly concerned that the sea would be rough on the Mediterranean ones, but to my delight it wasn't rocky at all. The only night i felt anything was on the first night and i put this down to the fact i was getting used to it.
The Grandeur is one of the older ships in the Royal Caribbean fleet and therefore doesn't have as many facilities as the newer ships but to be honest i don't think i would've has time to use them anyway. There is a teenage club for ages 12 to 17 in which they split into two groups, 12-14 and 15-17. I am 15 so i was just in the eldest group. I thought the activities would be quite lame but they weren't. The entertainers mostly leave it up to you what you want to do and they just sit there and chat with you. I found myself making lots of friends and sitting in the Jacuzzi until 1am! My mum never saw me which to be honest i think was good.
The food was amazing , i read before i went one review about the grandeur where a man was complaining about the service and the food however there isn't one negative thing i can say about my experience in the dining hall. The waiters and assistant waiters did everything we wanted and were fully deserving of the tips. The head waiter had lots more tables to watch over and we only saw him once throughout the whole cruise. I couldn't fault the food at all.
The windjammer is the other place at which you can eat and the only problem there is , it is quite small on this particular ship , so it is always busy. My advice on this is , pick the correct time to go in. Most days you'll have been off the ship anyway so by the time you get back on it will most probably be late afternoon. This is the ideal time to go for lunch especially if your on second sitting dinner time. The windjammer will be quiet and you'll feel full until dinner time. Of course if you do feel the need to have a snack , there isn't a promenade on this ship so the snacks are served in the solarium.
For anyone who, wants a short Mediterranean family break royal Caribbean is definitely suited to you. I wouldn't worry about the kids having nothing to do whether they're 5 or 15! They'll enjoy is most probably more than you and you may not see them much which gives you the time to watch shows , gamble in the casino and relax.