If you have an in-built air fan in your home, you will first want to examine it for safety. Make sure the heater us turned off and then carefully feel around all the vents. It’s best to wear some sort of glove while you do this to protect your fingers.
Check for any sharp pieces that would cut your toddlers fingers. You should also check that the heater does not get so hot that it will burn your child. Children have much more sensitive skin than adults so if it seems warm, that could burn your child.
You may want to consider surrounding the heater with a protective gate. If you do, put the gate far enough away from the heater so your toddler cannot reach over it or through it and touch the heater.
Another option is to use a sturdy fireplace screen attached to the wall on each side of the heater.
Don’t forget about checking any floor heater and fireplace surrounds for burn hazards.