When kalani and riley went through the mental instatute to reach the hospitals back-up generators. They encounterd "ink" , it was descibed as having fingernails on the floor. Perhaps "ink" is the one which cause the "little ones" to have nails filed down to a razor sharp point (as described by lizzie when the mallers convoy was attacked). They were also descibed as having a number FRESHLY tattooed onto there forearm , perhaps it was "ink" that has created these "little ones" and as the first "little one" number was only 5 this leads me to believe that the "little ones" are sparse. However this could just be a coincidence.