Communication during Cruise

If you mean your kids are on the ship also and you want to be able to communicate while all onboard, then as others have mentioned, the app is the cheapest and easiest way. If you mean your kids are back home and you want to be able to check in, you can get a social media internet package which would allow you to message them on WhatsApp or Facebook, or a more expensive package which would allow for iMessage, more internet surfing, etc. The social media package might also be a good option even if you're all onboard if you like to share photos or updates on your social media during the trip. But either way, you have to spend some money to have communication capabilities while on the ship at sea.

We spring for internet on 1 device and we're able to message, call, or video chat with family back home. Kids love it.

This is the way to go. We used on our last cruise and found it very helpful in keeping up with others in our party. Once you have the app downloaded and the $5/line, turn the phones to Airplane mode and leave them there, and you'll not spend any more $$$ chatting with each other. As JusMe said, texting is expensive...do not use this while on the ship, you could buy another cruise with the bill you could get. There are some internet packages if you must keep in touch with folks back home, but they are costly and service is not the best.

Cell phones and texting will work on ships but it is VERY expensive. Most ports will have cafe's that offer free Wi-Fi for texting or calling the kids back home.

Looks like you will be on Carnival. They have an app (carnival hub app) each one of you need to download. It has a chat feature where you can text each other. It is a one time $5.00 fee per line for chat service. It will be helpful in a lot of other ways. You can check your onboard account, see what is going on around the ship and look at dinner menus.