Most fish stores won't take fry until they are at least 1/2cm in length & can eat proper flake food without it being crushed. That's just the experience I've had with them. Unless of course you go there & they have some fry in a tank (sometimes the female livebearers at an lfs
give birth there & the staff put the rescued fry into their own tank) then you can ask if your fry can go in with theirs.
The fry will be freezing their butts off in that container so here's what I would do:
1.) Remove the mother from the hospital tank & put her back in the main tank.
2.) Put the fry into the hospital tank (as long as there are no other fish in the hospital tank)
3.) If you have a filter that has slits in the sides, put a pantyhose (I think that's what Americans call them) over the filter to reduce the chances of the fry getting stuck in the filter. It's not nice having to wash a fry out of a filter sponge :'(
4.) You can feed the fry on newly hatched brine shrimp or keep crushing the bottom feeder tablets.