It really depends on the type of toad. Cane toads for example if they find themselves in a dog's or child's mouth can kill them if it becomes ingested and goes untreated. The toxin's of Bufo toads are produced in those large gland behind their eyes.
If squeezed or stressed enough any Bufo toad will produce a white puss looking substance that oozes from these glands. I've never personally seen it shoot out but I imagine with enough stress and pressure it would be possible.
Just be sure your grandson knows how to handle the toad (not squeeze it) and keep the dog away from any direct interaction with it and everything should be fine. Toads are a pet you guys shouldn't be handling much anyway since they are very sensitive to the oils and salts on our hands. Their skin is so much different then ours.. they even drink through it! :P
Don't let this all turn you off from toads, they are a wonderful and usually very hardy pet for children if these couple precautions are followed.