I think he was trying to show people that he loves children so much. The Secret Service were near the spectators at various times, but it could be that positioning themselves right there at that exact time was so the camera wouldn't catch it if his hands started to stray.
Where can we get the video?
https://www.youtube.com/watch?v=v6rP8zpdiWU
Thanks!
The relevant time in the video is 41:25. https://youtu.be/v6rP8zpdiWU?t=2485
I think he was trying to show people that he loves children so much. The Secret Service were near the spectators at various times, but it could be that positioning themselves right there at that exact time was so the camera wouldn't catch it if his hands started to stray.