A group of moms, mom to be's and their assorted spawn. They generally travel in groups of 3-5 and anywhere between 5 and 15 offspring.
They can be but aren't necessarily more obnoxious than normal. You can generally hear the ruckus a block away.
They are also often associated with nice asses and tight fitting yoga pants. Not so bad if you've got noise cancelling headphones.
I was trying to work at the local coffee shop but the baby brigade rolled in at 11am and shut me down.