If you are only feeding them starer crumbles they don't need grit. If you are feeding them ANYTHING else, then they would benefit from CHICK grit.
You can buy a 5 lb (which is a LOT) bag at feed/hardware/country stores for $5 or $6 - OR! You can dig them up a little box of dirt from their future run area (the grit will be the rock particles bigger than grains of sand - do make sure there is some of that. Or drop $6 at the hardware store). If you haven't given them a dirt box yet I'd highly recommend it because it's both a great health/hygiene benefit, and it will help address your next question!
You got it! I'm surprised they're not being more feisty

The dirt box (with grit!) if it has insects and bits of weeds and grass in there... they will go bananas for it! They'll even play keep away games with what they find in the dirt! Hilarious! And kinda magical...
Do you have roosting bars for them to perch on?
We alleviated boredom with a "dangerous" choice; in the daytime (while we were ACTIVELY watching them) we'd take the lid off the daytime play brooder so they could perch and roost on the rim while we did afternoon/evening chores and did the dinner thing. They appreciated the scenery so much that they really didn't cause constant escape problems. There were a few days we just had to lid them up, for sure. but only 3 or 4. And they were in our living room for the better part of two months. Which leads to your next question...
...but first I'll say we tried mirrors and cat toys for entertainment, they didn't care for them one bit. I did NOT try a chicken swing and later learned that almost every adult chicken that enjoys a chicken swing, had one offered and played on it as a young chick. If I could do it over I'd definitely try to devise a safe, fun chick swing. On to the next!
Our first flier (her name's Amelia, hehe) had a vertical leap of 10 inches on her first day. Her bigger sister (both are barred rocks) was always the master escape artist, though. She flew onto the rim of our brooder (the same as yours? 20 inches tall?) in the first few days. All of them could get out in the second week. I think by weeks 3 and 4 they could fly four or five feet easily!
So most assuredly they will be escaping. I'm a little surprised they haven't already!
Again ours really just loved roosting and snoozing on the brooder rim for a long time. We let them know they were not allowed on the floor (or on anything else) outside the brooder. They would hope in the brooder to play and eat, etc. But the rest of the time they (mostly) just snoozed or watched us from the top of the brooder.
But they WILL escape. Make sure you have a clamped or heavy "lid" on top of the brooder that keeps them in whenever you're not actively watching them. I made one out of wood scraps and hardware cloth that worked very nicely. I'll add that pic in a few minutes....