Actually this started with the kids of smokers. But with that said, I’m in full agreement with you. This stuff has to end.
If a parent or parents were beating/burning/sexually abusing a child... take the child. If a parent or parents were allowing a child to starve, wander the streets as little ones etc... take the child. My point is if there is direct abuse/neglect then the child is in imminent danger. This boy is in danger of possibly getting high blood pressure or possibly having heart disease. Social Services... if they really wanted to help this boy would give the Mother access to a nutritionist (I’m sure there are government ones already) and advise the Mother to take him to a gym with a trainer (someone trained in exercise/the body etc). There is a good chance that this boy will NEVER be thin (it may not be his particular body type and metabolism). He could be healthier but not fit into the exact range on a chart. IMHO.