My son stepped in a rusty nail, we managed to pull it out, it went in about 1.5cm, hes been in pain all night. ?

Would expect it: You don't mention age but at any age that depth of penetration is enough to involve deep structures of foot ligaments/tissue. The chance of a deep tissue infection is real. Good cleansing of the wound & close monitoring are important. A review of tetanus status & booster if needed is important. If it went through a shoe or moist tennis shoe it may have really bad germs from that source.

Wound care: Tetanus shots are usually required every ten years, but if offending agent is really dirty, tetanus may be done at the five year mark. Puncture wounds can often become infected. It sounds like this nail penetrated quite deeply. Have medical assessment of the wound with wound care may be prudent.