Having taken on 5,6 and 7 year olds at parties (bouncey castles are ace cos you can fling them about and they don't get hurt) I think they would quickly learn to hang onto your legs. Once they do that it's surprising how few it takes before you can't move them. Once they do that they'd have your arms and before long it'd be lights out. If you could keep moving and take them one at a time then I'd say 50 odd. But as they will all swarm at you in the first few seconds I reckon 20 could take a decent sized bloke down.