This site says that my great grandma had three children. Betty my grandmother and Kathy who died a year after she was born. but they also say she had a son named Lennie Charles Blackmer on 28 th Feb 1937 and died that same day. It makes sence because my greatgrand mothers fathers name was Lennie.

My family has no idea who this boy could be. There has never been any thing said about him and I can not find a death certificate. Is it possibel there is a mixup?

Where are you seeing the info? In someone's Public Member Tree or in the OWT? In which state did this occur? Sometimes when infants die the same day they are born, especially back in the 1920s and 30s, there were only birth certificates and no death certificates, and sometimes they have a special category of death certificate for fetal deaths. Depending on which state you're researching, there may have been neither a birth or death cert. during that time period. Check nearby cemeteries to see if they have an infant buried with that name.

And if you saw this on the OWT, yes, its very likely a mixup.