We have never had a big problem. We get a table first and drop off carryons etc... then the kids and 1 adult go get food and drinks, and then when one person (kid or adults) comes back, the other one leaves to get their food. The first time we sailed we got onboard at about Noon and it was crazy...after that we managed to get on earlier and earlier in Boarding group 2 and 3 and it was much easier.
We also, go right to the Aft elevators instead of trying to use the midship elevators. This can save time.
Something to know about the buffet is that there is no real line, and many people will not understand this at first and get angry at you when you dart in and out to get food that you want.
For example, if you are in a line that starts right and meets in the middle and you want to get some French fries that are in the middle, but nothing else, just jump in and get the fries. As long as someone else is not going for the fries at the same time of course.

Instead, folks just go along in the line and wait until they get to the one item that they want. And then keep staying in the line until they get to the next thing that they want, which might be pizza.
I would actually recommend checking out where everything is at all the stations, as they wrap around to the very back of the ship. There is pizza, burgets, chicken nuggets, potatos, rice, noodles, and then another little section with soup and another with seafood. And yet another towards the back with hand carved meats, jello, desserts, yougurt, fruits and veggies. Check it all out first and have a plan.

Usually there are CMs there to guide folks but many times people don't understand that the CM is directing them to just go to where the food is that they want. We are programmed to be polite and Disneyfied, so it is a big adjustment. It took me quite a few cruises to just feel okay with jumping in. And honestly, when I see a little kid trying to get what he/she wants, I tend to let them get in there before me.