A recent study on the natural sun protection of these products found that many common food and spice oils have an SPF between 2 and 7.5. You can find it here. Authors Chanchal Deep Kaur and Swarnlata Saraf found that good old olive oil has one of the best SPF factors, at 7.5. Coconut oil is close, at 7.1, and lemon grass oil, which also keeps away mosquitoes, has a natural SPF of 6.2. There are claims that other oils have higher SPFs, but to date I've not seen exact figures, however, raspberry seed oil and date seed oil rate as similar to titanium oxide, a sun block, for skin protection, according to a study published in Food Chemistry magazine in 2007.
What does SPF mean? It stands for sun protection factor, and it means that the product will allow you to stay in the sun that many times longer without burning. So if you put olive oil on your skin, and you normally would get a burn after 15 minutes of direct sun, olive oil would allow you to stay in the sun a little under two hours, as long as you remember to keep applying. Now I wouldn't recommend pushing the limits of the SPF for your skin or your baby's but a layer of one of these oil before a dip in the water may help prevent sunburn, just stay well within your time limit for safety's sake.