I'm not sure about particular agents, but I did read in the Children's Writer's and Illustrator's Market that there has been an increasing interest in children's non-fiction, especially about unique topics. For instance one book, This Sucks, talked about different animals suckling, air presure etc. Machinery is a common topic in children's books so it would have to be done well to be origional. I'm not sure if there is a book out there that is about the dump specifically so that might work in your favour. Also, unless you have professional photography skills, editors probably won't want you to include your photos but instead have their own photographer take pictures.
There are mixed opinions on whether or not to try and seek an agent for a first book. Some sources say it is easier to catch a publisher's attention initially (i.e. one accepting unsolicited submissions) than it is to catch the eye of an agent.
Let's see what some of the more experienced people on this forum say. I am not very knowledgeable about books for younger children.
-Laura