The back rear tires will not keep air in them. How do I fix them or do I need to replace them? (Baby Trend Jogging Stroller)
More than likely there's a leak, maybe small but enough to cause a flat.
As for tubes your local bike shop may carry the 12" or the 16" depending on the stroller make and model. Check the side of the tire to see if you can identify the size, if not the stroller manufacturer or the site should give you more information.
The tires with these jogging strollers come off fairly easily with any regular bicycle tire levers. Although it's possible to take them off by hand, if it's difficult any bicycle shop would carry standard bicycle tire levers. I personally recommend the life time warranty tire levers by Pedro. They are very strong and designed to take off some of the beefiest mountain bike tires.
It would also be good to have spare tubes. You can find bulk tire tubes on eBay for cheap!