Your chicks are trying to tell you they need more space! Six chicks in a space smaller than eight square feet is going to be a big problem for them. You need to think about moving them into their coop asap.
Meanwhile, your chicks would be able to handle periods away from their heated brooder to enjoy romps outdoors. Choose a sunny, calm day of 65-70F and let them run and get in some low level flight. If you have a big backyard, they'll have a blast.
What I used to do, back when I brooded indoors, was to load the critters into a small pet crate. Then, once outside, I opened the door to the crate and hung back and watched them. It would take several minutes for one to get brave enough to step out, and then all the others quickly followed. They scoped things out first, then took off.
Don't worry about them running away! They will keep the crate in sight and return to it when they begin to chill. Once all have gone back inside the crate, then just close the door and carry them back indoors.
Try to let them out for these field trips every day, gradually increasing the length. Also, after a few days of these excursions, they will be able to handle cooler temperatures, also. By the time they reach four weeks or so, they will be adjusted to the cooler temps and should take the move to the coop with ease.
As they become acclimated to cooler temps, they will want to stay out longer, and eventually, it may be a problem getting them back into the crate again. While you have them outside, it's a good idea to train them to come to you. Use a favorite treat in a container that you'll use every time. Also use a verbal cue of your choice each time you call them. Chicks will learn very quickly to come to you when they see and hear those cues, so you never need to chase your chickens and try to catch them. All I need to do to get my chickens back into their run is to hold up the little white carton of meal worms and all twenty are inside in a mater of 60 seconds!