What temperature is it where you live? If it's warm enough, you should let them outside, either enclosed or not. But they need to be under supervision at all times. The chicks will be able to tell you when to bring them inside; when the get cold, they will start huddling together and will cease to be as active. I would love to see some pictures if you decide to let them out!
I start my chicks with field trips at 2 weeks old. As long as the day temp is above 55 degrees, no wind and the sun is shining, it does them good to get out and forage. Start out at about 10 mins and work up the time from there. Always supervise them constantly as they can get lost and be hawk bait as well. Helps to break up boredom as well. Make sure to offer up grit for them if they eat things other than their chick food.
I have three week old chicks that are staying outside all day but are brought in at night. Please understand that it has been 70 - 80 degrees and there are about thirty in each pen so they have been able to stay warm. Chilled chicks contributes to pasty butt and lowered resistance to disease. A good alternative is to bring in some clumps of spring grass with roots and soil attached and let them explore and sample that awhile. It not only keeps them busy but innoculates them with a little of whatever you have in your soil. Have fun!