The type of cast you are referring to is called a hip spica cast. It does indeed keep the child from bending at the waist or hip. The involved leg will have a cast down to the toes as well. The other hip will be casted but the knee on that side will be left free to bend.
A special opening or window is left in the spica cast to allow for bowel and bladder functions. An absorbent pad is placed under the edges of the cast for toileting. Many parents use disposable diapers for this task. For larger children, adult Depends can be adapted or cut down to size.
It is important to keep the cast from getting wet with urine or soiled with feces. The pads must be checked and changed often. If your child has full bowel and bladder control, then a bedpan and urinal can be used at the appropriate time.
Many parents adapt a child’s wagon to use for TV watching, transportation, and eating. Although there’s no bend at the waist, the child can be propped up with pillows well enough to eat and drink.
The nursing staff will give you precautions and tips for keeping your son’s skin safe. There are some problems that can be caused by the cast if it is too tight or ill fitting. Any complaints or signs of irritability must be checked carefully to avoid complications.