Trying something New- "litter training"

I have never done this before, but a friend said she did with just one litter of puppies, and it worked with them.   I have put out a tray of pellets for the puppies to potty on.  It is not working yet, but their feet are small and I can tell it is a little tough for them to walk on these pellets.   I have been putting them directly on it when they wake up so they pee there.  It has been hit or miss.  Some of them walk off the tray and then pee.  I will continue working on this and hope that they eventually get it.  I think it could really be a nice way to begin the process of teaching them "where" to go potty.