This is exactly what happened with my 350 stepsister and her three kids.  The younger two are between the ages of four and nine and are still at a healthy weight.  Her oldest daughter who is 14 though is fucking gigantic. Neither She nor her husband work, they just stay home eat and smoke pot.   Her house is like something out of Horders but a tiny bit better.  She claims her hypothyroidism is the cause for her weight, yeah sure Jan.