Been running two adventures this far with my young son (almost five years old) with the Old School Essentials rule system. It’s a modern layout of the old B/X rules.
Its been working great this far and we have played both Winters Daughter and the one-pager Please go to sleep, Arthur Cobbleworth.
We added some minor house rules to make things extra fun:
- Crits: On a natural 20 on an attack dice we double the damage roll (we thoroughly enjoy the mini celebration every time you get that sweet 20 on the dice)
- 0 HP: When a character reaches 0HP we do not instantly kill him. Rather he passes out and we make him permanently injured by loss of an attribute point.
I will add to this list as we discover more things we’d like to tweak.

“Did you ‘take care’ of the demon possessed parrot?” - “no, we killed him”. Today we played the one page adventure “Please go to sleep, Arthur Cobbelworth”. As per usual my son solves everything with brutal honesty towards every NPC.