Alright little buddy, a regular constraint is like a set of rules that you have to follow so that you don't get in trouble.
Think of it like a game of hopscotch: there's a specific pattern you have to jump in order to win. If you don't follow the pattern, you lose the game.
In the same way, computer programs have regular constraints that tell them what kinds of data they can or can't use. For example, a program might only be able to use numbers between 1 and 10, or it might only be able to use letters of the alphabet.
If someone tries to enter data that doesn't fit within these regular constraints, the program won't understand what to do with it and will either give an error message or not work properly.
So, regular constraints are just like rules that programs have to follow so they can do their job properly. They're important because they make sure that the data is organized and accurate, which is crucial for any program that is supposed to help people with something like math, science, or even just entertainment!