Good morning from ChickyGoldens, My 5 girls are just about 6-1/2 weeks old. I have them in their new chicken house and they love it. I have a heat light hanging for them but they never go under it. Temp inside is anywhere from 50-58 in the morning. They went out there on Mother's Day (Last Sunday) now that they are acclimated, I want to open the hatch door to explore there protected outside yard.
They do not need that heat lamp, day or night. I'd turn it off or unplug it now and take it down as soon as reasonable.
We call that a pop door. I'd open it and walk away, they are ready. I've had all chicks leave the coop and be on the run ground within 15 minutes when I first opened the pop door. I've had some groups wait until the third day before the last chick actually went outside. Same breeds and mixes, same coop and run. Groups of around 20 chicks. Each group is different, each flock has its own dynamics.
Your problem may be to get them back inside at night to sleep. They've been in the coop for about a week, that is often enough for them to accept the coop as where they should sleep. But sometimes they still don't go in at night on their own. Mine often put themselves to bed under the pop door in the run (my grow-out coop is elevated). I wait until it is fairly dark so they are easier to catch and toss them in on the coop floor, then lock them in for the night. Sometime they catch on very quickly and put themselves to bed where I want them to but I've had a couple of broods I had to put them in every night for three weeks before the last few got the message. Each group is different, each flock has its own dynamics.
Is it okay to give them grub worms now and some other treats? The feed store I go to said to wait until 20 weeks.
Some people that work at the feed store, a grocery, or a clothing store know what they are talking about. Some do not. Guess which you unfortunately talked to.
One of the first thing a broody hen does with her chicks is take them to a place where they can peck at the ground. This has different benefits but one is that they obtain grit. That is small bits of rock that go in the gizzard so they can grind food that needs to be ground up. Then she takes then to eat. They eat whatever they find or she finds for them. That can be vegetation, bits of stuff on the ground, or creepy crawlies. If it is too big for them to eat she breaks it into pieces for them. They need the grit so they can grind that stuff up if it needs grinding, but there is no reason they can't eat it.
You are not a broody hen. You will be feeding them chick Starter of something similar. That chick feed contains all they need for a balanced diet. If they eat too many treats you can upset that balanced diet. The rule of thumb is to only give then treats that add up to 10% or less of their daily diet. I don't have a clue how you measure that so I use a different rule of thumb that says if they cannot clean it up in 10 to 15 minutes it is too much. Treats are fine, just don't overdo it.
If they forage for much of their food you have given up the ability to micromanage their diet. Instinctively they do a pretty good job of balancing their diet as long as they have some options (and they usually do) but still keep the special treats to a minimum.
How do I add grit to their diet
Your ground probably has what they need for grit so let them outside to peck at the ground. Or you can buy grit at the feed store for them. Some people offer that grit in separate containers and some toss it on the floor of the coop or in the run. They will find it.
and some dusting for their feathers.
You read a lot about that on here but many people have tiny runs with bedding covering them. If they have access to the ground they will dig their own holes to take a dust bath. That's what mine do, dig their own. Some people mix dirt, sand, ashes, or whatever in a container for them to use. I don't so I can't give you any specifics on that.