I just noticed that my son, who is 7 months old, has small bruise-like spots on his back. They are located on his upper left butt cheek and somewhat along his spine (almost in a row). We have a nanny, but she seems to be good with the kids (I also have a 2 1/2 year old). He does not seem to show any signs of discomfort when he sees her, which tells me he feels comfortable around her. Should I be concerned?