[strawberryfields]

Here's just something to keep in mind: You should definitely look into the child gate or the doorknob protector, to keep your sister and the hedgie safe. But remember that, should she get into the room, a three year old isn't very likely to harm a hedgehog. If she frightens the hedgehog it will just become a big ball of quills, so she is more likely to get hurt than the hedgehog is. Instead of trying to teach her to stay away from the cage for the hedgehog's safety, teach her that staying away from the cage is to keep her from getting hurt too. Some children are more likely to listen when they find that their curiosity can cause them harm.