This is an instar (nymph) of a shield or stink bug (order Hemiptera, family [Pentatomidae])(https://en.wikipedia.org/wiki/Pentatomidae).
This appears to be similar to the 2nd (or possibly 3rd) instar of Halyomorpha halys.
European and Mediterranean Plant Protection Organization; Credit: Matteo Maspero
UTIA suggests the 2nd instar begins to develop an almost black appearance, where that blackness gradually shifts to browner shades in subsequent instars. According to Medal et al. (2013)1 the 2nd and 3rd instars have median lengths of ~2.75 and ~4.25 mm, respectively. According to WSU Extension, instar nymphs of H. halys are spiny (including on the shoulders) and possess light bands on the antennae.
Source: WSU Extension
This University of Wisconsin Extension site provides a fairly similar photo to your specimens, which can be found at bugguide.com:
Source: bugguide.com; Credit: Yurika Alexander
1 Medal, J., Smith, T. and Santa Cruz, A., 2013. Biology of the brown marmorated stink bug Halyomorpha halys (Heteroptera: Pentatomidae) in the laboratory. Florida Entomologist, 96(3): 1209-1213. PDF