Your coop looks very well built, nice job! But....9 chicks? That won't be enough space when they're 6 weeks old or so. Might want to start a bigger coop with a run now.
There is a respiratory disease that can be transmitted through the feces and dust. I know my GI doctor had a kitten fit when he found out I was shoveling out coops without a respirator. I was wearing a bandana mask, but he said that wasn't good enough. I now use a respirator (like you find on the paint isle at Home Depot) and that has appeased him. It is only a problem for those with compromised immune systems, but it is something to think about. Just don't let the kids shovel out the poopy coop and it shouldn't be a problem. Other than that, I think you are fine.
I ordered nine chicks in the hope that if I ordered more than I needed, some would die in transit, or during the first week or so, knowing my luck they will all survive, then I guess I will be building another coop! - I went on the measurements that each bird needed 10 inches or perch space, (Im sure I read that somewhere) so I was hoping to have 4 or 5 chickens in here.
I also have a chain link run for them, about 8 foot by five
I've handled a lot of chicks and I've noticed that my skin is getting brown spots and becoming quite wrinkled. Of course the fact that I've been doing it for over six decades may be a factor.
Perch space is important, but there's a lot you're leaving out. The chain link run will help. If chickens are too cramped they will start picking on the weakest bird.
On your theory of buying more than you need. I did the same thing. Only 1 died and I had a lot to rehome. Roos are tough to rehome and some ended up in the freezer.
My kids handle ours often. I keep some Germ-X on hand, and nobody has ever gotten sick from ours. Cleanliness is important whatever the animal being handled, but chicks are not more dangerous than puppies IMO.
Do you home school your kids? Schools and hospitals = breeding ground for bad diseases, not baby chicks. Hand washing is the key to a healthy lifestyle period. I've been around 100's of cases of H1N1 this year, never caught it cause I'm a zealous hand washer. Just regular soup and water is best, watch were there fingers go when they handle them; no nose pick'n or eye rubb'n or sucking on fingers. Any portal of entry
I think it would be torture for the little ones not to have some fun with the baby chicks while mom and pa had all the fun.
I put more eggs in the incubator hoping I'd get 20 chicks.
I got 41!
Yeah, you'll need to get a bigger coop. You'll use the one you have for isolation or for a brooder in the future.
I wear a surgical mask every week when sweeping and mopping the coop. I've had mycobacterium before and it's a nasty cough like bronchitis that lasts for MONTHS.