I think you could safely say my chicks are very sheltered. It was a huge move for me to start brooding them in the coop. But, I have watched mama hens take their babies out in the snow on day 3!!!Interesting. I have always provided grit from day 1. But then I have also introduced mine to the outside world at a young age. I call them "field trips" to the yard. Once it is warm enough during the day they will be out in the grass in a run enclosure to meet the bigs and experience grass and bugs.
My mums have always tried to get the chicks out into the world around day 3 or 4. I usually hold them in the coop and porch until they have a full set of wings as the ramp to get back is a challenge otherwise.
So I try to replicate that for the chicks I hand raise.