Before I start, please read this with the mindset that I am not angry with you, just upset. Heres why:
My opinions on plugs are close to that of Walkers and a few others that have posted. That haing been said, doing what you did in the manner that you did it was wrong. The corect way to go about that series of events would be as follows. Explian your veiws on BBDs to the two, then offer to trade a bag for there plugs. If they decline, explain that at this feild plugs are not allowed, then give them the bags (IE let them keep the plugs)
What you did instead is borderline to THEFT. Please relize that, and in the future go about your actions in a diiferant way.
Now What to do with the plugs? Well for starters if you can find the two and give them the plugs back, do so. If not then either keep them in the event you do see them or give them to the feild owner at the event you were at, with instructions to give them back to the kids. Now there are tons of GREAT ideas on how to recycle plugs, allready posted in the event that you obtain more of them by right ( Ie trading, finding, or purchasing)
Personaly I always use my plugs (when allowed) and not my bags ( with the exception of my Vector as it has a AA loudner on it ) and except when required, or asked by someone playing with my group to use a BBD,I dont plug/bag my nelspot at all. I come from a firearms background and hold the value that if the safety is off and you pull the trigger and the gun (or PB marker) fires, it is loaded. Incedently that is why I dont care too much for revolvers. Same goes for my nelspot, I can pull the trigger all day long and unless Ive cocked the gun (aka Loaded it ) it wont fire. Anyway I relize that IM probly beating a dead horse here. Just Remember that Im not so much upset with what you did, but how you did it.