Hey Jeff,

Looks like you have an aphid infestation. Those are very common and can destroy a plant fairly quickly if you don't take steps to get rid of them. You didn't say what kind of plants they are but you should probably:

Wash under running water - run the foliage under water everyday and rub off as many as you can. This can usually keep the infestation under control. Also it helps to use a dilute amount of dish soap in water, say like a teaspoon per gallon of water.

Spray - You can spray with an insecticide made specifically for houseplants. This is usually very mild stuff but you're advised to apply this outside.

 Here's a helpful link to Houseplant Insect Control

Cheers,

Pat