Ask for support to arrange the fundraiser. Approach the children's school, or speak with other parents about organizing an event together. That way, you can share the workload.
Hold a meeting with the volunteers, and invite the kids along. Explain that you are holding a fundraiser, and include detailed information about how fundraisers work. Ask the children to come up with ideas for generating money for charity.
Settle on a quick, simple and feasible idea that requires little cost in set up. Hiring a bouncy castle would be great, but your profits will be lowered by the rental. Face-painting, cake sales or fancy-dress during a school morning are ideal.
Delegate tasks to one or two of the adult volunteers. You need to organize a date, gather supplies and invite local kids to the fundraiser. This can be arranged within a couple of days with little effort, so explain this to the volunteers.
Meet at the agreed location with the kids and the fundraising supplies.
Explain to the group how you will organize yourselves. For example, for a car wash set up three or four wash points. Allocate teams of four or five kids, supported by an adult volunteer and supplied with buckets of water, car shampoo and sponges.
Ask the kids to have direct contact with the people who are attending the fundraiser. Get the children to explain why they are raising the money, and let them take payments.