Forget the 5-econd rule. For kids, it could be the 5-day rule or the 5-year rule. They just don't care.
You could stick a nice, juicy steak in front of my daughter and she wouldn't eat it right now. But let her find a day-old Cheerio in her carseat or a Teddy Graham the vacuum missed, and she'll happily pick it up and pop it in her mouth. I'm rarely fast enough to stop her.
And the thing is, she never was a big one for putting things in her mouth. She didn't chew on toys or gnaw her hands a lot. She didn't pick up anything sitting around and chew. But her food is a different story. She's been a good eater since we figured out how to breastfeed, and once she discovered rice cereal and other baby foods, she was quite happy to shove those in as well.
I'm happy to give her these cereals or crackers as snacks. I don't even flinch when she picks up food she threw on the floor and then eats it after we let her down from her highchair, before Daddy grabs the vacuum. I know what's been on MY floor. It's just pretty gross when you talk about eating a stale piece of cereal that's been hiding under a toddler's rear, in a carseat, for a day or two. Or, heaven forbid, in a parking lot or a store. Gross.