Yup, those are aphids. That type attacks my tropical milkweed all the time when it is in bloom. My geraniums act as barrier so it does not move to the other plants. I just try to hose them down or use alcohol/diswashing liquid solution swab or spray it directly while the sun is not yet hitting the plants.
Just editing to add: if you have ladybugs around..they would love those aphids big time!
