Over the summer we also ordered an aquarium kit for Kitty, our daughter. It took weeks for them to arrive, but then we had order fish eggs and brine fish eggs and salt to feed them to complete the kit. The eggs are for killifish. They are a type of fish that lives in small ponds and streams in the "wild" that might dry up, so the eggs can survive for weeks until the rains come and the water returns.
The fry (baby fish) are about a week old now. They are only a few millimeters long but the baby brine shrimp are even smaller. The fry are transparent, so when they eat a shrimp, you can see their stomach in addition to their eyes. We will see how many live to be adults.