We are in the same situation at our school. Last year we tried a mother son beach volleyball luau type of party, with little success. We think it's because the grade levels were 3-5.
This year we are trying game night. Setting up lots of "minute to win it type of activities"
Wish us luck!

C couple years ago for a father/son night we had a karate teacher with some of his students do a demonstration. They talked on self discipline and control. Afterwards the boys got to practice kicks with their equipment. The boys loved it. It was really inexpensive to do. Usually if it is within our budget we get something for the moms. A couple things we have done are a color spot of petunias or marigolds, or a sample bubble bath.

Hello,
One thing that our school has done is mother/son bingo night. The PTA serves refreshments and gets prizes from Kipp Bros. or Oriental Trading, finds some items for the moms also(dollar store), and invites the mothers and sons to an evening of fun.
Hope this helps!

OUR SCHOOL RECENTLY HAD A DAD/DAUGHTER DANCE AND IT WAS GREAT. BUT NOW I AM STUMPED FOR A MOM/SON ACTIVITY.WE HAVE ABOUT 120 BOYS AND ABOUT 1OO MOMS. KINDERGARTEN TO 5TH GRADE, WE HAVE 500-600 DOLLARS TO SPEND. THANK YOU,LAURA