How many adults to supervise at 7th birthday party?

[QuantumWeatherButterfly]

DD turns 7 in a couple of months. We've arranged an art and craft party for her. It's being run by a professional provider, at a hall we have hired. DH and I will be there, plus the woman leading the art activities.

The minimum number of guests we have to pay for is 15 (including DD), though we can have up to 20. While I assume we can have fewer than the minimum if we want (as long as we pay for them) DD is unlikely to be persuaded to that.

7th birthday parties round here seem to be the time when they become drop-and-run affairs (which I'm fine with, as I've benefitted!), but as DD is our eldest this is new to me, so I'm not sure on the general supervision levels needed. Given the age and number of attendees, how many adults should we try and have on hand? Should I be twisting grandparents arms to help out?

If you have 20 children attending, I would probably want at least 1 other adult more so in case of emergency

In a hall, where noone would be going outside I think 3 of you would be fine. I'd probably get another 1 or 2 people to help with the setting up of the food.

I think 3 adults for 20 7 year olds in manageable so wouldn't panick. Especially as doing a craft rather than running around.

If there is a family member who would enjoy attending I would ask them though.

3 adults is fine, 4-5 ideal I would say.

Thanks, everyone! Grandma has agreed to come and help out, so there will be 4 of us now. Thanks for your kind comments, I feel much better about it now.