Apartment Balcony Railing Cover?

My balcony on my 2nd floor apartment is very sterdy, My son is almost 2 and I can see him from the window while Im inside.. but I still feel alittle weary about him being out there without me. The railing is about 4 feet tall.. I want to find something maybe like... mesh? or some kinda cover were He wont be able to stick any arms or legs out in between the bars.. Or throw any toys over. What would one of these things be called? Or where would I be able to find one?.. I dont think my apartment would allow any kind of lattice or something non see through