I'd personally really hate to give up a rare evening of free time at an event like that, I'd much rather have a day where I can spend it with my family doing something.
My mum runs fundraisers for a local charity, and whilst it's a different type as it's for rescue dogs, the same sort of concept can be applied to a fundraiser for a pre-school.
Look for a suitable field, if it part of a school use that one, then hold parent and child obstacle races that charges an entry fee, with rosettes and a grand prize for the winning team.
You can ask for donations from local shops in exchange for publicity, they can even pay extra to 'sponsor' the games.
We charged for entry £3 an adult and £2 for children, however for a school fundraiser I'd probably have it a little bit lower until it's established.
She found an up-and-coming band to do a free performance for publicity by appealing on Facebook, all she was asked to do was provide a stage and make a few announcements about them every now and again. She asked someone who helped the charity, to use connections they had to get scaffolding to make a stage.
You can put out a call for companies to pay to have a stall at the event, at the last couple of events I've helped at some even donate a portion of the profits to the charity, and you'll get quite a few takers usually.
We've had fun fair owners wanting to set up bouncy castles and other rides which appeal to children.
You can find people who want to be food vendors, we've had pizza places, curry sellers, vegan places and all sorts, so something for everyone.
It is time consuming, but she managed to organise it alone, and had about 10 on the day helpers, whilst she had a full time job and other commitments so between a few people it's is more than doable.
The main thing is finding a venue, then it's sourcing skills that are there within the pre-school parents, such as someone who may have links to a printers for posters so you can advertise around town.
There may be some initial costs but you can keep them down as much as possible by buying second-hand.