My boys both have very sensitive skin too. I bought this last summer and have used it a few times: Amazon.com: Avalon Organics Baby Natural Mineral Sunscreen, SPF 18 , 3.5 Fluid Ounces (100 ml): Health & Personal Care
It is kind of pricey, but it was cheaper than that when I bought it, so maybe there are better deals out there.
I like that it's a mineral sunscreen, not chemical, and it's unscented and paraben-free. It does go on kind of whitish, but that's not that big a deal.