Warning: adorable, squeezable cheeks ahead. Some good friends of ours have six month-old twin girls and were kind enough to let me practice taking some photos of them in the park yesterday morning. I think a few of them turned out pretty well - I've never had the chance to try and get two babies in focus at once.
For just learning how to sit up, I'd say both of these girls look like pros after only a few days of practice. Watch out - crawling is just around the corner!