I've helped a friend to do this but not for profit, we raise a small amount for the school each time.
The most important thing we have learnt is to have 1 major item for the children to do with a small back up item as well, don't give the children too much choice because they tend to want to do one of everything. In your advertising make a big thing of any theme you are doing and/or suggest what they might want to do in advance in the way of planning their design.
Our school are happy to send out flyers in the childrens bookbags, we also do confirmations for each child with a reminder of anything they need to bring or do in advance. Always have a few aprons or old shirts handy because there's always a few children who forget.
Scour ebay for bulk buys of materials and equipment, much, much cheaper than Baker Ross.
A bit more specific, but one of our best recieved sessions was decorating a shoe sized box (purchased flat in packs of 20 from ebay) somewhere on the outside was "Look inside and you will see, something very special to me" and inside the box was a little mirror, dead simple and went down a storm.
Cheap shower curtains make really good table protectors.
I think that's most of it 