Step kids calling you mum by accident - how to deal with it?

[SteppingOnToes]

It's not long since I have met my partner's kids and things have been going smoothly so far - they seem relaxed with me and are nice kids. Yesterday we were had finished colouring in pet rocks and shoe boxes for them to live in, we were sat on the sofa watching cat videos with his 5yo son snuggled up to me. He asked me a question and accidentally called me mum by mistake. He didn't seem to realise he said it (and neither did his 10yo DD who was sat on the other side of me) and I didn't say anything - I didn't want to make a big deal about it and potentially upset and embarrass him (we've all been there when we've called teacher mum/dad and it's mortifying).

But the question is - if it happens again WTF do I do?!?!

Disclaimer - I don't have children and have never dated anyone with kids either so this is all new to me...

I have been called everything ie mum, dad, granny by my dn. Mum is a word that most kids use so many times in a day that it usually just slips out without them thinking.

My children call me Grandma when they come home from her house. Then laugh and tell me I have less wrinkles

They have once or twice called me Daddy when they've been at his house. I was tempted to sell them for that

My Dsc do this sometimes, I just carry on as I know they mean me and it's a slip of the tongue.
My kids also do it to my other half, my little one in particular often calls him dad as she hears his kids call him that. Again we just don't react.

My kids also often call me dad by mistake on and off for the first day or so after they get back from their dads.

I think you're reading far too much into it. Why do you think he called you mum?