Anywhere milkweed is growing you will eventually notice red and black bugs in residence. To the casual observer they all look similar, but once you actually look at them you can see there are a couple of species that are quite different.
On my milkweed I have lots of Longhorn Milkweed Beetles (Sometimes also called Red Milkweed Beetles, but not by me. Who could look at those antennae and think the defining characteristic of the bug is red? Seriously.)
I also have tons of Milkweed Bugs. (Also called Large Milkweed Bugs, so as to distinguish them from Small Milkweed Bugs.) These guys are fertile. They are always getting busy on the plants when kids come by and ask about them (every freaking time, I swear) and the babies swarm about on individual milkweed pods fairly routinely. Here is a picture of an adult and a juvenile together, as well as a pic of the babies en masse. Did you know that baby bugs are called nymphs?
I’ve seen Small Milkweed Bugs, but very rarely and I have no photos. They are smaller than the Large Milkweed Bugs (natch) and have a slightly different pattern, with two dots on their backs at the tail end.
Longhorn Milkweed Beetles and Large Milkweed Bugs are completely harmless to everything except milkweed and are not a concern in small to moderate numbers. They don’t eat much.
I don’t have much personal experience with the Small Milkweed Bugs, but I have not read anything to indicate that they are harmful to people in any way. I have read that they sometimes eat Monarch caterpillars, but have not been able to confirm that from a reputable source.