When my sons were a toddlers they were always bumping their heads. They're still pretty top heavy at that age I don't think that helps the situation.
DS2 was especially prone to it a few trips to the hospital prone! I thought for sure at hosp visit #3 with him when he was 2 we would get investigated, but they seemed to understand that he was just a toddler
He's 15 and now no permanent brain damage