I think these are harlequin bugs (possibly nymphs).
Harlequin bugs belong to the Jewel Bug Family (Scutelleridea). One of the distinguishing features of this family, is the large scutellum, which covers (in some species) the entire wing, giving the appearance of single dome.
The scutellum is the third division of the thorax (the middle division of an insect, between the head and abdomen) viewed from above.