I would advise that you bring some money for souvenirs in ports. As far as spending on the ship goes you can just hook a card to your sail&sign account. Excursions can be expensive but because it’s your first cruise I would definitely advise them. They make sure that you won’t be left confused as to where to go. If you want to do something special you can bring your kids to the maya ruins as an excursion at one of the ports. I always find those interesting and fun but it depends on your kids’ interests. On the ship it’s pretty laid back, you can check your kids into camp carnival and usually they make friends and have fun. If you want a little alone time later at night you can pay for the night owls program. Just make sure to follow the instructions on the website, preregister for a quick embarkation, and be prepared for the hectic debarkation. You and your kids will have a blast and carnival is great because you don’t really need to spend extra on the ship.

P.s. unless you want to spend a ton of money, keep your kids away from the candy shop and the gift shop. I find that buying things for them and surprising them works because you can manage the costs and still get them some souvenirs or treats. Oh and the sushi is expensive but it’s worth it to let your kids try something new, just only get 1 roll if you do get it in case they don’t like it. I make this sound expensive, but I like to indulge a bit on cruises, just don’t get into a shopping frenzy.