Hello!
For a topic like this I would recommend using one of the larger databases that we have access to. Go into our LibGuides at www.libguides.brenau.edu and choose Databases A-Z which is located in the section called Guides towards the bottom of the page. From here choose Academic Search Complete. In Academic Search Complete, I chose to use the advanced search. In the advanced search I limited the search to full text by clicking on the full text box, limited the search to scholarly/peer-reviewed articles by clicking on that box, and limited the results to the dates 2007 through 2013. I used the search terms "physical education" AND obesity AND "school children". In the advanced search, Academic Search Complete adds the word AND in between each search box for you so you will not have to type this in but you will need to remember to encase the search terms physical education and school children in quotation marks so that the database knows to search for those words together as phrases. Here is what your search should look like:
I got some good results with this search. Here are two examples of articles that I found:
Ramstetter, C. L., Murray, R., & Garner, A. S. (2010). The Crucial Role of Recess in Schools. Journal Of School Health, 80(11), 517-526. doi:10.1111/j.1746-1561.2010.00537.x
Milne, E., Simpson, J. A., English, D. R., Johnston, R., & Giles-Corti, B. (2007). Time Spent Outdoors at Midday and Children's Body Mass Index. American Journal Of Public Health, 97(2), 306-310. doi:10.2105/AJPH.2005.080499
Be sure to look through all of the results to find what is most helpful for your research.