Are your kids watching YouTube of other kids play Minecraft Mods?
The Minecraft Demo Mode version Java Edition is Free
Before you install Forge or Mods be sure to backup your Minecraft worlds first.
There are three game modes in Minecraft, Creative, Survival and Hardcore.
You can building other things after you have collected or mined materials you needed.
Minecraft is a sandbox video game. Sandbox means it is similar to kids playing in a 'sandbox' where they build and tear things down.
You can install different versions of Minecraft Forge and Minecraft Mods without uninstalling previous Forge or Minecraft.
The Best Minecraft Forge to Install
There are two things you need to do before you can install mods.