A doctor can tell if your child has hand-foot-and-mouth disease by the symptoms you describe and by looking at the sores and blisters.
Roast the beets for 50 to 60 minutes. Cook the beets until tender, checking them by inserting a fork into the center of each beet. When the fork glides in easily, the beets are tender enough to remove from the oven.
Place the sliced raw beets (allow 1 medium beet per serving) in a foil-lined baking dish and drizzle with a bit of olive oil. Bake at 400 or 425 degrees F. for 20 to 30 minute or so, until tender to your liking.