Hi Snailguy,
If the tank is cycled and has no betta they will be fine. I have currently got baby platies in a 2 gallon tank with a heater and a sponge filter. I just ran the sponge filter in the main tank for a week then filled the 2 gallon with water from the main tank. I do water changes twice a week changing about 40% using dechlorinated tap water and they are doing fine. Once they get about half an inch long i move them back in with the adults.
On the other hand when i first had babies i put them in a breeder net and they started dying after about 3 weeks.
At the minute i have 13 in the tank 6 are nearly a centimeter long the rest are a few millimeters. Within the next week though i hope to bring my 15 gallon from my mums house and move them in there. Along with some baby bristlenoses if i can catch them.
Hope this helps
Emma