This is really cute! I liked the idea of playing from the slime/monster POV (there's actually a TTRPG I've played with my kids with similar protagonists called Rainbow Mutant Slimes!) I also liked that each of the monsters in the party had a pretty clear role (fighter, healer, etc)
The tutorial at the beginning was VERY thorough, but I honestly would've preferred it broken up into a couple of separate sessions, maybe running between different sparring partners if you want to keep the same vibe as after the story mode has truly started? I also may be a bit dense, but was there a way to use the healing items between fights? I wasn't able to figure out how, although I was never really in any danger of losing a party member, so it wasn't too big of a concern.
I like that Enemy Plans can be toggled on and off, I feel like that could give the game a lot of replayability with an optional boost in difficulty.
It's also really cool that you used your kids' artwork in your update!