How old is the youngest? Are they both unable to hold it or just one? Is it diarrhea or solid? Could be that the younger pup needs to go out more, or if diarrhea is involved could be a matter for the vet to figure out. Pedigree actually isn't the best dog food though, you should check out the foods forum
http://www.pets.ca/forum/forumdisplay.php?f=53 there is tonnes of good advice there on which foods to choose.