We have never had a guard around our wood heater and have never had any problems. The kids would go near it of course, kids are kids, but it was too hot for them so they left it alone.

My ssiter has a metal guard around her fire which gets really really hot. Her son burnt himself once on it and has never gone back to it. Another friend of mine used a playpen which she altered so it only has 3 sides and can fold up in summer. So I'd recommend using a wooden playpen instead of a metal fire guard.