I'd bet that's a wren, they love using tiny sticks where other species would use grass, feathers, etc, and they love the small entrance holes like that.
Also, wrens like to build more than one nest, in different locations, so it's not unusual to see a wren nest where the adults might be at or near a nest often, but never lay any eggs in it. Not sure if the spare nest is to confuse predators, or maybe provide a place to lay another clutch of eggs if the real nest is wrecked.
Not baby's this time, just a nest. If it's the same bird as I seen a couple three weeks ago in the same spot, they are black and dark blue. Really fast darting fliers.