Q For Mummys With Little Boys

hi i have a 2 1/2 year old and have just noticed a small white lump under his foreskin right at the top of his penis. i am a bit concerned as it seems to move with the skin as if it is a type of cyst. is this normal? or is there anychance it could be the part where the wee comes out and is just slightly swollen? i have never pulled it back as i didnt think it should be done yet but am now worried i should have been cleaning behind there and that this might be a bit of infection?? at what age do you do that? or teach them to do it?? please helpx x x x