wait, how old are the kids? Can they ride bikes?
If you just want a trailer to haul stuff check out the 29er BoB Trailers.
... or take any decent kiddie trailer (including this Nashbar kiddie trailer, http://www.nashbar.com/bikes/Product_10053_10052_168065_-1_201459_10000_201460 on sale with 20% coupon for $72...NO BRAINER!!!) and just gut it for cargo use... According to the specs, these trailers have a higher weight capacity than many cargo trailers, and in many cases cost LESS, so why NOT convert this??? You may have to reinforce the base a bit, but the basic frame setup is already there... PARTY TRAILER!!!