Wow Lori that's great. My kids would love to do this type of stuff regularly. I am afraid I am not as open minded about leaving science experiments about the house as I would like to be. Gee they do make a mess! Interestingly I let my kids paint inside, use playdough, goop and any number of other messy things but the mess is always away by dinner. Unlike the science project mess which lasts weeks!
My kids do enjoy making little habitats ( usually with my good baking dish...
) and will have a go at mixing any thing with water to see what happens.
I am inspired by your post to be more open to the mess and set up a little area in their toy room for this type of thing. We never seem to have any trouble growing mould here.....high humidity means the bread only lasts a couple of days before we get either green or white mould on it. ( never both colours I just realised....)
Keep it up