Often times I see people blame the broody hen, but really it needs to be a two way relationship. The chicks need to find that warm spot under her, and she has to have that motion under her to flip the broody hormone to the taking care of chicks hormone.
Pipca is right, if you want her to hatch, do not slip chicks under her now. Wait till she hatches those. Not all of the eggs will hatch, and some of the chicks may not make that she hatches. This happens even if you get chicks, with in two or three days, there can be chicks that failed to thrive.
A lot of time, people wanting to be helpful and with the best of intentions interfere too much with the process and confuse both the chicks and hen, and they get upset and take the chicks away.
Chicks can and are stepped on, and most do just fine with it. It is not uncommon when a chick sticks their head out, to get a peck on it to get the chick back under. Let them work it out.
In the beginning I worried about the other layers bothering her, and not enough about me bothering her. Now I just leave them be. Maybe standing just inside the door listening for peeping.
Mine have always left the nest in about 24 hours, those who have hatched have done so, and the rest are a no go. She will make a nest on the floor for them, so I have clean bedding a day or two before the expected hatch.
I really don't think your week old chicks will go under the hen when the others start hatching. They have learned the heat lamp.
Mrs K