Heating coop question

[supermom]

I have 3 barred rock chicks. They are about 7 weeks old. One of them seems to have all its feathers and the other 2 have a tiny bit of fuzz left on the neck but mainly feathers. They live in a box in the garage at night and are outside during the day. I want to move them into the coop with my other two chickens that are about 18 weeks old. I live in northern CA and the nights are about 65 degrees. Can I move them out? Do I need a heat lamp? How does one attach a lamp so they don't burn themselves?
My coop is a converted dog house on cinder blocks (with a roost bar inside and two eggless nest boxes attached to the side)

 

[debilorrah]

We have a lamp that hangs over the side of the brooder and they get right up underneath it. I was afraid of them burning themselves at first - until I saw them pecking at the bulb!! But, yes they do still need a lamp - they like it warm, the warmer the better. Plus they need 12-14 hours of light every day and with winter approaching, a light is best right about now.