Just tried a little experiment (very unscientific) with my two kids (ages 13 & 11). I had them put their heads in my hands, I am a female with pretty large hands. My 11 year old's head seems to be about the size of the skull in the photo.
ETA: They are both girls.
Interesting! I was hoping that someone would be able to do that. My daughter is three and her head is smaller that what I could tell about the skull found. I think it is a child but an older one...Not a toddler.