The first image doesn’t do anything for me, but the second one shows a lot of promise, so I’d like to comment a little more on that.
For starters, I’m not bothered that I can’t see their faces. Yes, generally we should see the subjects faces if the shot is to have any impact at all. But every once in while it’s good to break the rules and it can result in a cracking image. I think if you had gotten down really low with a wide angle lens (and closer up), you would have had a much stronger image – the kids would have been bigger in the frame, you would not have had the trees on the horizon and the kids heads would have stood out nicely against the sky instead of partially blending with the field. OK, I know it’s not easy to think of these things in the heat of the moment. I’ve got two kids myself and know that they don’t usually hang around long enough for you to get a good shot. The only solution I’ve found so far is to just be as prepared as you possibly can be and shoot loads and loads of frames (unless you’re shooting film where you might need to be a little more conservative with your shoot rate)