I think if you strip 5E down (i.e. leave out a bunch of player character details/options) you'd be fine.
Keep the 6 ability scores. Adjust those yourself based on their race choice.
Give each race one feature/power
Maybe dump some classes, but regardless just come up with super-clear, short descriptions ("wizards study hard for their magic, warlocks get it from a powerful creature, sorcerors just got lucky one day!"). You could give them all the same hit points, or start them at max HP for their class. Don't confuse them with hit dice, all the class-based proficiencies, etc. Make as many class feature choices for them as you can, and then just tell them "you're a fighter, you have the "second wind" feature, so you can get some HP back all of a sudden, but you'll need to rest for a good while before you can do it again"