They aren't born with any grit in their system - grit comes solely from them picking it up either from a container offered by you or their environment (for those who are out and about). The time when to start offering it will vary depending on who you ask - because it depends on when you intend to offer anything other than chick feed. They won't need grit as long as they are strictly on chick feed because they can digest that w/out grit - ANY food stuff other than chick feed, though, and they need grit. So, if you start offering "treats" (veggies, egg, etc) you need to provide them with grit....whether you do that at 1 week, 2 weeks, 6 weeks, etc is up to you.I bought a bag of chick sized grit but the bag says they don't need it until they are 2 weeks old. I found that very interesting. Maybe they are born with enough grit to digest for a spell?