I think Pedants' Corner is the right place to ask this. There's something about the expression "mum to 3 boys" or "mum to George and Molly" that grates and I don't know why. It's that word "to".
Surely, the standard usage would be to say "of", as it's a relationship, as in "husband of the Prime Minister", "son of John and Mary", "brother of...".
The "to" seems a bit too earnest (?) or makes it sound like a job (?) or as if that's all that defines that person: "I'm just a mum to two small boys" (I suspect "I'm just a dad to..." arises less often). I can't quite put my finger on it. I feel like I first encountered it in trendy magazines aimed at parents, eg something from the NCT, but that would have been some years ago.
Do I just need to get over my hang-up or does anyone have any sympathy with my reaction?
Pedants' corner
What are your thoughts on "mum to 3 boys" v "mum of 3 boys"?
DadDadDad · 25/04/2019 23:27
It may just be an association with a certain kind of "smug" parenting from when I first encountered it.
"Yeah, I've got a kid, a boy actually, and he's going through that terrible toddler stage"
v
"I'm mum to Bertie and we enjoy going to tiny tots sing-a-long every Tuesday..." ("we"? you, as a grown-up intelligent adult enjoy trying to sing 'one man went to mow' while for the twentieth time dragging your two-year old back into the circle... - sorry, I'm ranting now... 
).
I think I agree with you, and I also don't quite know why 
I am, in fact, a mum of three boys - and that's how I'd always say it. Never 'mum to three boys'. It just doesn't sound quite right.
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