Halloween Trick or Treat bags

Hello everybody, I want to make some trick/treat bags for two little kids in Portland, Oregon. The oldest, a girl is now 3, and I figure she is old enough to 'get' Halloween, (and Christmas, in due season). The baby boy is just one year old but I know his big sister will want to know why he hasn't got a bag, unless I make two. BUT, as Halloween is not the big deal/industry in Australia as it in the States, I have no idea how big/small the bag should be. I thought I'd use the Drawstring Bag from Little Things etc (my very first pattern from my new book) but the dimensions seem rather large for littles. Can any of you very experienced Halloween mummies or daddies help me out, please? I need to make these suckers asap to get them posted in time. I'm also working on a Halloween quilt for the same reason, but that's a different story.