My guppies were born the end of January and are about 1-1/4" long while the platties born about the same time are only about 1" long. The platties have a larger body than the guppies. I have swordtails born within a week of them and they are slightly smaller than the platties. They are in a 55 gallon U.S. tank (about 20 or so fry total) with 5 adult platties, two adult swordtails and one adult female guppy. It sounds like your fry are doing OK.