Where are you going? The studio should have all the appropriate props. Even Sears, Wal Mart and JC Pennys have good props. If you are having them professionally done just take your childs favorite toy and a couple of cute outfits. A picture under a big tree on a blanket is a good one. It's hard to do them that young because they don't get out in the sun that much to do things. Sitting in a sandbox is cute. The studio near us had lambs there when i took my daughter Good luck.
Beach ball, sunglasses, the bucket and shovel set for a sandbox, beach unbrella, butterfly net, flowers, just a few ideas... Also it is really cute to get the pics taken with a few of the baby in her swimsuit, we just did that a few weeks ago, turned out really nice.