Lucie had one I noticed when she was about 4 months - behind her ear. It was a dermoid - basically just a cyst and nothing sisnister but they can eventually become painful and infected (but it could be when they are 2, 20 or 50 - no one knows!) so they cut it out when she was about 8 months old. It was a quick day surgery op and no dramas at all and you can't even see the scar now. They'll probably ultrasound it to check out what it is. Good luck.