Protecting child from wall heater
I'd place some sort of wall/fence around the outside. You could use two or three segments of a gate system like this:



Or for a more DIY solution, you could build a fence on a plywood base with rubber feet to hold it in place.

I would not recommend using heavy furniture to block access, as it will (1) block heat circulation and (2) in the event that your child does climb over it, he would be less able to escape.