This is an odd way to go about this for sure.
Here's what foster parents that "I" know have on hand.
They have an organized area/room for clothing. They have it hung and in drawers by gender and size. Diapers and baby things are in their own area since most of them won't hang.
Over time they've "collected" from garage sales, hand me downs from friends, and taking advantage of great sales and added to their storage items. Plus they get a stipend each moth for each child. That money is to purchase and pay for anything that child needs. One foster mom makes sure all the kids have their needs met then spends the rest on household bills. That covers things the kids need too. She also spends a bunch on groceries. She has no "income" per say but she does get to keep anything she doesn't spend on the kids. Again, their needs are met and some extras are also provided too.
Whatever she buys for a specific child is that child's property. They take it with them when they leave. They also get emergency money when that child is first removed from their home and placed with a foster family.Those items are that child's items and they get to keep them.
As for stuff for the kids as far as toys, they need to be aware they should never allow the little ones, under age 3, to play with the toys meant for bigger kids. Such as Barbie shoes, they are a serious choke hazard for little ones. Gummies are choke hazards too. They have to keep stuff put up and out of reach for any little ones they might have to bring in.
They can buy good things at garage sales over time also. If you want to purchase specific items for kids then do that.
There are so many issues with what they're thinking here. In my opinion they are biting off a lot more than they can handle. Do they seriously think they are suddenly going to get that many foster kids? The mom will have to not work because she'll be running these kids from court dates to parent visits to doctors appointments and more. They'll likely need helpers too.
I do think they have a good heart. If they understand the goal is always to re-unite these foster children with their parents. They are in for heartache if they think this is adoption time.
As for furnishing their new space that's very expensive for sure. I see where they're coming from as far as their shower requests. They are asking for help in that area. Maybe you can contribute a little towards a furniture fund then get a couple of things specifically for the future kids.