My platy fry are over a month old now (born 19th December), they had been living in a plastic hatchery tank and were growing up. Some are much bigger than the others, one is massive its nearly 3 times bigger than the smallest one.
I have now placed the fry in a bigger tank, my 18x10x10 (Clear Seal) tank and they swimming about fine, they also got my 3 frogs as company as moved them there too.
I think I can finally tell the sex of one of the fry, the largest one seems to have a dangler!!, i can no longer see the fan fin like all the others do, but not 100% sure yet. My orange platy which I thought was a male turned into a female overnight when the fan fin appeared so the large fry could still be bluffing and just pulled its fin upwards.
I had saved 7 of them a month ago and all 7 still survive.
Here is a quick video of them although quality not that good!, the rest of my videos/images of them growing up are on my blog listed below.