You can take them off the medicated feed and give them the plain chick starter. Eating grass and bugs will not give your chicks enough nutrition to survive in a healthy way. You will see lots of health problems as their deficiency takes effect. Baby chicks are fragile. They need to be taken care of and protected. They are a responsibility not to be taken on lightly. They certainly are not getting tired of their feed. It is exactly what they need.
I may be wrong but your post reads as if you may be tiring of the chicks. Perhaps they should be rehomed?
My chicks are about 4 and a half weeks old, I wouldn't put them outside yet because they dont have all there back feather in yet. If you feel like your chicks are bored, then have you ever gave them a couple hard boiled egg yokes?
My chicks go crazy for them and my kids and I get a good laugh.
If you put them in a coop they will need to be kept with a heat lamp in a draft free enclosure until they fully feather out. Most chicks don't get mature feathering to keep themselves warm or to regulate their body temps until 8 - 10 weeks. Some breeds need 12 weeks to feather out. Until then they need to be protected, kept warm and in a draft free area. They do need chick starter and will need it until they are 18 to 20 weeks or until they start laying at which point they will need layer ration.
You can put them out supervised for very short period to scratch in the grass and play in the sunshine but you have to watch them for chilling. If they get chilled they can get sick. It can even be fatal.
If they eat very much grass and such you need to over them baby chick grit to help digest by grinding their food as it passes through the gizzard.
How do you know if a chick is chilled? What are signs to look for? I have moved my chicks outside, they are in a doghouse with a wind-block for drafts but steps to get in and out if they chose (they haven't chosen to yet). They are 4 wks old. They did great last night, when I went to check on them this morning they were all laying next to each other (not huddled up in a pile). We have a very small house and just couldn't take the dust anymore. (My husband has allergies) so I did my best to make a safe setup for them outside. They have a heat lamp in the doghouse, straw for bedding and their food and water all in there too. I have 15 of various breeds. Sorry to hijack the post but it seemed to fit here (similar topic)
If they were chilled they would stay huddled together and not move around much. If you're babies are running all over the dog house, eating and drinking and not just hovering under the heat source for long periods of time they are probably fine. I don't know how big your doghouse is, but if you have 15 in there, I bet they start to venture out soon!
My 1850s book on chicken-rearing said to feed chicks chopped grass and dandelions even when they're very young to keep them healthy. I don't know the nutrition of it though. You just have to make sure it's chopped tiny. I just cut a bit up with a scissors or knife and gave it to them (a little bit) and they loved it, so I did it every few days. They had other food as well, of course.