If Mom is staying out of the box this early, she is probably too warm. If you are using a heating pad, she may need a larger "nest" so that she can get away from it and still be with the pups. Actually, if your litter is out of drafts and in a warm room (above 70 degrees), a heating pad should not be needed. The only time I use one is if puppies are weak. Are the smaller ones gaining? Weigh them once a day - if they are gaining even a small amount, you are fine. If not, you need to either force them on a nipple or supplement feed them. If you don't have a scale, get a food scale that weighs in grams/ounces. If you use the ounce weight, make sure it will read in 10ths of an ounce. Even the small ones should be gaining a couple of 10ths of an ounce every day. Also check to be sure if they are dehydrated. To do this, gently pinch the skin on the back just behind the neck. The skin should go back down on its own. If it doesn't, the pup is dehydrated. Get some calf liver and simmer it in 2 cups of water for about 20 minutes. This makes liver water. Remove the liver and let the water cool down. Give the pup a few drops every 30 minutes or so.
Never give young puppies any type of supplement not made specifically for young puppies. Too much of a good thing can do more harm than good.
Best of luck with your litter.
Charlie Farrar
Evenstar's Yorkshire Terriers