Blame it on my French roots but I cannot imagine how anyone can take their mother out for Brunch on Mother's Day at 10:00 am.
Any week-end but this one, no problem.
I am afraid that if I did that to my mother on that special day, she would refuse to talk to me for a while.
In my opinion, having a meal that early on a holiday makes it look like a chore that you want to get done with ASAP.
It smacks of bad manners.