Traveled with my twin sister and her family (husband and two small children ages one and two) and my husband and my kids (12,10,8,8). My husband and I are in our mid 30's.
Tips: 1) Don't do parking across the street if you have a lot of luggage and children. Our parking lot was across the street but we had LOTS of luggage and it was hard to get it to the terminal. We paid 45 but an extra 15 would have been worth parking right there.
2) Babysitting for under 2 year olds does not start until 10 PM. By that time, you don't feel like going out because you are exhausted from your one year old...lol
3) Book all of your excursions when you get to the port. When we went to Jamaica, we took a taxi (3 a person) to the Sunset Beach Resort and Waterpark. The day passes were around 70 for adults (all inclusive) and 35 for kids. This is much cheaper than doing the resort excursion through Carnival which I believe was 100 or more. The kids loved the resort and the waterpark/slides. The food was ok...The drinks were ok. We drank red striped beer most of the time.
4) We booked the carnival sting ray tour for $65 a person. It was good but expensive (6 people). A couple we met got off the ship and found an excursions to stingray city for $25.
5) Cozumel was by far our favorite port. We got off the ship and walked a few blocks to a resort called El Cid La Ceiba. The sign outside says 70 for day passes but they are really cheaper. We paid 45 for adults (our 8 year olds and 10 year old was free) and we paid 25 for our 12 year old. You get unlimited drinks/food and 90 minutes of snorkel equipment. Bring your own goggles and you will love it. We spent most of the time snorkeling. The alcoholic beverages were great and the food was pretty decent. This was definitely a deal.
6) MAKE sure you do self check out in the deembarkementation process. Don't leave your bags the last night. In the morning, take all of your bags down yourself and you will get of the ship early. We were tag #'s 23 and it took forever to get off. We didn't get into our car until 11:00 AM. We spent almost two hours on the 9th deck waiting. Many people with numbers after us got off early anyway and did not wait for their numbers to be called.
7) The camp carnival was good but our kids that were the oldest in the group did not have as much fun. Our 8year olds are almost nine (in a few months). The activities in that age group are geared more towards the 6 year olds.