We give candy to whomever comes to the door. And if it's a tiny little kid with his/her parent or older brother or sister, we always insist that they help themselves as well.
I do give double takes when someone comes in plain clothes, no costume, but I don't begrudge them a piece of candy. Life's too short to worry about it. I just shrug it off.
What I won't do, however, is just let a kid stick his/her hand in the bowl. MAN, kids get greedy! LOL! I dole out a piece or two at the beginning and then give out bigger portions as the night wears on so we won't have any left in the house after.
All that said, where we live, we don't get many trick or treaters at all. Few years, we didnt' get a single one, other years, we'd get three or four tops, last year, we hit a record and got about 20 or so.
This thread reminds me of when I was a kid. I'd always been tall (6'4" now) growing up and when I was 11, my friends and I went out for a night of trick or treating. We were all in costumes that we made, most were pretty cool to look at it. I had made a huge pumpkin head out of paper mache, spray painted it, cut out the jack o' lantern holes, wore a white sheet over my body and called myself The Great Pumpkin. Very proud of it!
We went to one house and the lady opened the door, gave everyone candy, then looked at me, nastily said, "Aren't you too old to trick or treat?" and gave me the hairy eyeball. I was a polite kid, told her I was only 11 and apologized for it. No idea why I was sorry I was 11 but what can you do? She then called me a liar and shut the door. I was so embarrassed and felt ashamed of myself.
First and only time we "tricked" a house when we were trick or treating.