So here it is.
Mehen is a Male. He just have long hair that's all.
Regarding the FL calling him Mom is like a figure of speech. Example could be: I introduce my female friends as "this is my bf". The abbreviation "BF" doesn't mean "boyfriend" but "bestfriend".
So the FL is just messing around (bcoz we know she is older than her actual appearance). She's just trying to act like a kid calling Mehen as her Mom because he took care of her and she sees him like his mom.(But not actually but to tease Mehen).
Mehen also doesn't deny it when FL calls him Mom because He genuinely feels sorry and loves her to the point that he doesn't care what the FL calls her as long as she is happy.
My half message got cut off omg
Here's the continuation.
The childcare team calling Mehen as Lady prolly might be any three of this reasons.
1. To go along with the FL, like going with the flow so that the FL is comfortable and happy to see others addressing Mehen as her Mom.
2. Either the team is trying to tease Mehen because they know how serious and strict Mehen is but he just doesn't care enough to correct them because he doesn't mind being addressed as Lady if it is to satisfy the FL's needs atm.
3. Translation mistake. (But I highly doubt on this, but welp will get to know from the novel readers or when the officials are released)
Is Mehen a woman or a man?! No, I didn't get confuse bc FL call em mom but the childcare team refers to as Lady Mehen????