With them a week old, I personally wouldn't try it. Hens can be pretty picky, I had a hen with 2 day old babies, and I tried to sneak 3 newly hatched babies under her in the night, and woke up to a completely scalped chick huddling in the grass alone with the other two chicks.
Also chicks bond in those first few days, week old chicks may have no clue who or what she is supposed to be.
It also depends on how long the hen has been broody. She needs to be broody at least a couple of weeks. And week old chicks are questionable.
But if you want to try it, here is how, add them in the dark of night, and it will help if the chicks are a little cool, so that they will be wanting a warm place. And the warm place will be the broody hen. HOwever, as the above post said, get down there early in the morning, in case it don't work. However, I just talked to a gal, who had this very thing WORK! Then hen had only been broody a week. The chicks were getting feathers, but it worked. We both know it was amazing, but sometimes you get lucky, and if so it is a great way to integrate into the flock.
Many people think that the relationship is one sided, as in all the broody hens side, but really it is a two sided relationship, the chicks have got to want to be with the broody hen, and she has got to want them.