We always did Donuts with Dad (then include Grandfather, Uncle, Male Guardian, etc in the tagline) as not to exclude anyone (same goes for Muffins with Mom just change the gender
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Some do just Donuts/ Muffins as a social event (your goal is just to get parents involved)
Some do alongside (ie bring/read a book, cangoods)
IMO the simpler the better - I think they both should just be a social (and maybe here's what the PTA/O's and school do and why parental involvement is important) not a fundraiser/ collection of any sort.
IMO school and PTA/O's should foster community/ parental socialization/ education as well as involvment - this event could fit 1- 2- or 3 ideas
Some RSVP (as to get a food count) and some dont