Hello, i understand your concern. As you rightly said, a small bump on the head usually occurs after hitting her head somewhere. Right now, there are two possibilities that I would think of. One, she hit her head without being aware or forgot about it which caused a hematoma(small blood collecton) which resolves on its own. Two, it could be a lymph node if the swelling is present near the lower hairline (usually behind the ear or above the nape of the neck). Lymph nodes in children are usually enlarged due to scalp infections/hair lice or dandruff. What you should look out for: 1. Multiple swellings occurring 2. Swelling becoming hard 3. Swelling persisting more than 2 weeks 4. High fever or loss of weight If none of the above are present, you can be reassured that there is nothing serious. Hope this helps you and your child. Do feel free to clarify any other doubts you may have.