(2) Before you play, create some ready PCs of various classes. Not all of them, it's enough to make a Fighter, Wizard, Rogue, a couple more if you wish. Make them as simple as you can, by picking the simplest (and shortest to read) spells and abilities. Then tell your kids what does each character do in general: the Fighter fights and defends his friends, the Rogue explores and finds dangers, the Wizard does magic. Let them choose which one to play, and decide only the name, gender and race*, and whatever appearance and personality they want.
*Use human stats when creating the PCs, and let race be only a cosmetic choice. Although, you could pick ONE special ability for each race such as Dwarf's darkvision, Halfling's luck or similar.
I quote myself because I want to explain better this point, which was my own choice but it can certainly be done differently
The reason behind it, is that I think it was important to give my kids a character
choice without having to do a character
build.
Character building is a major part of D&D but it will unavoidably stretch the time from when you manage to have everybody sitting down at the table to actually starting the adventure. If you don't have especially quiet and attentive kids, chances are it will become a mess while you try to guide all of them through it at once. If you want to absolutely do it, I'd rather take aside one kid at a time maybe some day BEFORE playing, and just build the character, so that everyone is ready on gaming day.
I went instead with pregens, so that I could give then simplest and most iconic character abilities, and just start playing in a few minutes. It still took 10-15 minutes for them to hear about 5 classes and fill the details.
About races, my decision was made to avoid having to do ANY modification to the ready character sheets, except for adding the name. Using human stats means no special ability, therefore simpler. I still wanted them to freely say they were an elf or dwarf or whatever (one of them chose a centaur!) for role-playing but that's it.
However, as I mentioned, it is also cool to have some difference because of race, but to avoid having to recalculate stuff on the character sheet, I would avoid stat bonuses, and just give ONE special ability chosen by you. This is something I have done for adult beginners, for which I have also typically used pregens.
A third option if you really want to use full race stats, is to simply pick fixed class-race combination. You then ask them to choose if they want to play the Dwarf Fighter, the Elf Wizard and so on. The character sheets are ready to use, but some kids might to play Legolas or Gandalf and be disappointed that the combination isn't there.
