Let him out of the stroller and follow him around doing stuff.
I think in the pictures you've posted it looks like you have him locked up and strapped down and confined so you can get a picture of him, it should be the other way around... you should catch him open in his elements!
I take my 3 kids with me on photoshoots! lol
Right now I'm not charging though, but once I start charging I know I'll have to find them a sitter.
Usually I go to a nice park, where they can play within ear shot. Sometimes they just sit in the van and watch a movie.
They are 3, 6 and 9. but my husband is deployed to Afghanistan and I'm also new to the area and so it just has to be this way for now.