Ay, momsh, that sounds like it could be a pilonidal cyst or something similar, definitely worth getting checked by the pedia or a dermatologist para sure, kasi hindi siya something to self-treat at home. A few of us mums had similar worries and honestly, the doctors were able to identify it quickly and give proper advice whether it needs treatment or just monitoring, so don't stress too much pero get it checked soon na lang para peace of mind mo!