I think the first one is a cockerel, going by the comb & wattles and also be the breast color.
If it's a bantam, it's probably an Old English Game Bantam, judging by the appearance and by what breeds are common. It's probably the color called Black Breasted Red. Males get a black breast, females get a salmon breast.
The second one is probably a Black Cochin bantam. I'm not sure about gender. With the comb and wattles being so small, it could be a female. But I think I see some bright red in the wattles (even though they are tiny), which could be an early sign of a male. A few more weeks will probably make it much more obvious one way or the other.
When identifying chicks, other than looking at the color, I find it useful to check specific details. Are there feathers on the feet? (Not on the first one, yes on the second one.) What type of comb? (Both look like single combs.) Any crest on the head? No. Normal feathering or Silkie feathers or Frizzle feathers? Normal feathers on both. Skin color? Sometimes white vs. yellow on the soles of the feet will narrow down the options, although I'm fairly sure of these two even without checking that.
Many breed-description pages, includings the ones at some hatcheries, will have a list or chart with such traits.