So I had an idea. So Mumbo is (possibly) the youngest hermit, if not one of, So I thought:

What if when Mumbo was around 5 he got lost, and the other hermits (ages 10 to 16) found him and took him in.

Notes:

•Mumbo is very shy at first but later on he gets to know them all.
•When they find him, Mumbo panics but someone (Grian possibly I'm not sure) calms him down and they find out Mumbo is attracted to the red glow of a redstone torch, literally like a moth  XD
•Grian = OVERPROTECTIVE BIG BROTHER
•No ships in this that involve Mumbo. He's literally like 5 years younger than the other hermits I'd feel very weird-
•All the other hermits are like 'What do we do with this child'
•When Mumbo's around 20 (15 years later-) his parents and siblings come to find him but he is not happy as it's been 15 years and feels like they don't really care enough.

Feel free to use this I guess