So today when I tried to play with my kids and wanted to have some family fun time I joined in with their game but then my 9 year old daughter lost her temper with me and shouted at me for ruining her fun and "mumming it all up" 
Mumming it all up - what does this even mean?
Obviously it was meant as an insult but I don't get what she was trying to say or how being a mum could be a bad thing. Can anyone shed some light on this for me?
Thanks x