I would be insulted NOT to be asked as a friend of the family (aka you).
Furthermore, if your space can accommodate it, allow for 'open invitations'/ tables to be sold. My mum goes to a couple of these a year. She rarely spends less than $500 and often spends as much as $5-10,000, as do most of her friends. These are ALL events that are put on where she has never met the family in need, but hears about them through word of mouth. Typically the 'goal' of most of these silent auctions is 25-100k, 10-20 tables of 8-10 apiece.
The Children's Hospital the child is at is always linked to the invite, so that auction attendees (or their lawyers) can call and verify that they child actually IS a patient of theirs (scams do happen).
When children are seriously ill, it's not just medical bills to be paid, but also rent/mortgage and childcare and groceries and bills that all need money... when suddenly one or both parents is now unable to work. These auctions are usually set up so that the family has money for their living expenses as well as medical cost, so that they don't lose their homes, can afford to eat, dress their other children, and worst case scenario have $ for headstones and funerals, ALL ON TOP of the actual medical expenses.
My son being in and out of the hospital for 6mo this year cost us 8 grand in copays, and apx 15k in lost income/added expenses and we live 5 MINUTES AWAY (aka not paying for plane tickets, driving for hours, etc.), only have 1 child so don't have added childcare expenses for other kids. Which is peanuts compared with transplant kids' families, esp when one parent has to quit their job entirely, family may have other kids, etc. Hugely difficult for us, financially, but not impossible. Versus my friends I made there, who their fully insured stays end up costing them 50k+ easily. Even double and triple that. The worst hit, being those that are underinsured. Middle income families who don't qualify for state aid, or charity aid, until they've lost everything. These auctions and benefits are trying to STOP that from happening at best, or to out and out pay for STUPID copays (like when you have to put 100k down for a transplant, or 20k for a surgery, because they're underinsured).
People in the benefit community GET that, and they come with their checkbooks at the ready. They won't hear about it, though, unless you REALLY get the word out there. Which means let EVERYONE know, and have them tell all their friends. Also, Talk with the hospital, they'll often have benefits (from yardsales to silent auctions) listed, which can get even more people involved.