If a child is to have the Service Dog, then you have a couple of options for siblings. If the siblings are old enough to have a lot of self-control, then best practice is to have the siblings not interact with the dog (which will encourage the dog to bond primarily to the handler). If the siblings are too young to have much self-control, then—it's not ideal—but we'll have to let the siblings play with the dog. (However, even in this case, you should give the handler and dog as much time together as possible so they can bond.)