A couple a month ago I was detecting a tot lot and a woman showed up with a little girl about 4 or 5 and an infant. They weren't bothering me so I kept hunting. The little girl came over and climbed up on a swing not far from where I was hunting and asked, "Mister, can you push me?" Right away I said "No, that's something your mom should do for you." and then started moving away from the swing set. Within a couple of minutes the mom came over to push her. I may not be the sharpest pencil in the box, but I'm not stupid.
A couple weeks later a boy and his dad came up to me while I was detecting in a different park. The kid was mostly polite and showed a genuine interest so I described what I was doing. He wandered off for a few minutes and then came back without his dad. I handed him a very small pewter statue I found in between his visits and he looked at it then stuck it in his pocket saying, "I'll wash it off when I get home." I must have had the biggest look of shock on my face he's ever seen when I said, "I'm just letting you look at it, I'm not giving it to you!"
Try to be nice and they take advantage. Don't be nice and you're the creepy old guy. We can't win.