They look like PLATY ( live bearers) to me. These breed as often as every 4-6 weeks with fry born live and free-swimming and up to 80 fry per batch. Fry grow quickly and it's easy to be overrun.
Scientific Name(s): Xiphophorus maculatus
Maximum Size: 7cms
Minimum Tank Volume: 60 litres
Minimum Tank Size: 24" x 12" x 12"
Water Temperature Range: 20-26°C
Water pH Range: 7.0-8.5
Water Hardness Range: 10-30 dGH