According to your description, (bumps that expel a “white thing” when pressed) your son might be experiencing a skin infection. It could be bacterial, but it's not certain. Warts are caused by the Human papiloma virus (HPV) but they don’t expel white matter when pressed. Skin lesions need to be seen to be properly diagnosed. You can bring your son to his primary health provider or even a dermatologist, if necessary.