Do you have the iWorks apps available?
If so, you could create s simple spreadsheet with graph, give it to each of them, and all they would have to do is fill in a number.
Or, you could do the same with a chart you create in KeyNote, and have them use shapes to add bars to the chart.
I don't know how sophisticated first graders are these days, but the app Explain Everything would let them create/draw a chart, and even record their explanation of what it means as a video. Doodlecast will do much the same, only a bit simpler. Doodlecast Pro has more tools, but still not quite as complicated as Explain Everything.
All of these apps will let you import a picture first, so you could still create the basic chart and have them draw the bars. The bonus of having them record their explanation is that it would help you confirm they know what they are doing, and perhaps stimulate interest in the project.
This is not personal experience. I'm not a teacher, just a tech who keeps an eye on a few teching/tech blogs because I find it interesting.
Good luck.
Here's a link to a podcast where Fraser Speirs discusses the use of Explain Everything with it's creator. You may find it interesting.
29: Explain Everything | Out of School
