No!!!
Oyster shells are there to provide extra calcium for the egg shells if they need it. But since yours are not laying, they do not need it. Once they start to lay, you can provide oyster shell on the side. If they want it, they will eat it. If they are getting enough calcium elsewhere, they may not eat any of it. I keep oyster shell out for mine, but with me feeding them layer, which has extra calcium in it, and them free ranging, they are finding all the calcium they need. They hardly ever touch the oyster shell and the egg shells are fine.
Too much calcium can harm a growing chick. It can cause bone deformation or possible kidney damage. Once they are adults, they can handle the extra calcium, even if they are not laying, but don't give extra calcium to growing chicks.
This means that your chicks should not be eating layer. It has over 4% calcium. At 7 weeks, they should be eating a chick feed that has around 1% calcium, or maybe just a bit more. That is all they need for good bone growth. I generally feed Grower at that age, but there are a few other options.
Chickens do not have teeth to grind their food, so they eat grit to use in their gizzard to grind up their food. For grown chickens, that grit can be a rock up to the size of a pea, but young chicks just need very small pebbles and large grains of coarse sand. You can buy chick grit some places, but beware of the parakeet grit you can get in a pet store. Read the label. Not all, but a lot of that has extra calcium in it. I just get coarse sand from my gravel road or the run and give them some of that. Play sand is too fine and smooth and does nto work.
If all you feed them is Starter or Grower, you do not need to provide grit. It has already been ground up and them reformed to make the crumbles or pellets. Their gizzard can handle it without extra grit. You can feed them some other things like boiled eggs or yogurt without giving them grit, but you should give them grit before you feed them about anything else. I start mine on grit about day 3 in case a hard shelled bug wonders inside their brooder or my wife stuns another wasp and gives it to them to play with.
Oyster shell is not grit. It is not really hard enough to gring up a lot of stuff, but the main reason it does not work is that the chickens digestive system produces acid, much like a human. The acid dissolves the oyster shell.
Good luck! Hope this helps.