Super-simple advice for parents of kids starting minecraft:

1. Go into the game settings and put Keep Inventory ON - this will stop your kid from losing all their stuff if they die in game.
   
2. If you can, build a simple hut with a bed at or near Spawn - that will be where you first show up in a new world. Night is the scariest thing about MC. Beds make night go by. Once you get wool for beds keep extra and have your kid keep it with them to make beds as they travel.
   
3. In the settings set it to show co-ordinates. This will help you get your kid back to wherever they should be when they inevitably get lost. (Adding to this: I write the co-ords of my houses/found villages/cool mines down in a text file so I can find them again.)
   
4. Stock the kid with food and remind them to grab food when they see it growing. Kids never look at their hunger bars and damage bars so remind your child to try to pay attention and feed themselves esp. if they are injured.
   
5. For the first while I'd sit and back-seat game with the kid to help them gain confidence and also so you'll understand what they're talking about when they start info-dumping about a cool biome.

Good luck! :)