This is something of locking the barn after the horse has escaped but:
The single most effective antimicrobial agent is 10% bleach. (Not including impossible things to do like autoclaving, taking things into the vacuum of space, etc.) That means 1 cup of bleach to 9 cups of water. We use it in labs to clean all surfaces. ((Note: we don't have wood in the lab.))
The SECOND most effective antimicrobial agent? Soap and water. Plain old soap and water. (Now here's the tricky bit... soap is 100% natural ... it's just fat and ash, BUT most natural "soaps" don't actually have any soap in them!!! Aaaargh. Talk about annoying. I couldn't figure out why we kept having stomach problems one month, until I realized the yummy smelling natural "soap" I had bought didn't actually have any antimicrobial properties. So we essentially had multiple cases of mild food poisoning all month -salmonella, e.coli, whatever. Double grrrr. If you look closely they're called "cleansers" if they're following the letter of the law, but many just call whatever they happen to be selling soap.)
Anyhow, the reason I say it's rather like locking the barn after the horse has escaped, is that when you bring people into your home, your entire home has just become contaminated. Yes. It's still worth occasionally washing all the toys (mostly for the biological contaminants, skin/food/mucous/etc. that act as food for pathogenic -aka harmful to humans- microbes, as well as just the yucky but not pathogenic ones, most molds, etc.
Now, most microbes have a short lifespan without a host. Minutes to hours. Others, like TB can exist quite happily in microdroplets hanging in the air from an infected person who speaks, coughs, sings, etc...for days. In some cases for as long as 2 whole weeks.
When you have a person over, or go over to their house, they bring all of their germs with them, and you bring all of yours with you. The best way to pass along an infection? Breathing. The second way is to be touching each other (shaking hands, passing an object, etc.). Since you can't get the kids to stop breathing around each other, and sharing by definition involves touching the same objects... whatever one has, the other will catch.
It's just the nature of being alive. And why people with compromised immune systems avoid other people, like, well... the plague.
Most of us have healthy immune systems. So keep sanitary, but don't go off of the deep end. And don't forget, the more we let our kids play in the dirt/etc. the healthier/stronger their immune systems get. So don't let a toddler crawl around on a hospital floor, or public toilet... but don't try and make them live in a glass bubble either. Both extremes are unhealthy.