XShares, the sponsor of the HealthShares family of ETFs, needs a big hit. Its new target-date exchange-traded funds, which offer one-stop shopping for investors with a specific time horizon, may just fit the bill.The five TDAX Independence funds, which were developed in partnership with discount broker TD Ameritrade ( AMTD) and launched on the NYSE Monday, are the first ETFs aimed at this fast-growing segment of the retirement market. They are also the first ETFs to invest in both stocks and bonds. XShares has struggled to find a market for HealthShares, launched in January, and has experienced some management turnover. Nat Wasserstein, president and head of development for XShares Advisors, left last month, just days before William Henson was hired as chief executive of the parent company, XShares Group. (The CEO post had previously never been filled.) The 19 HealthShares are possibly the least successful ETFs launched this year and an embodiment of how betting on highly specialized products to stand out in a crowded industry can backfire. Each Healthshare tracks a narrow sector of the biotech industry. As of Friday, the entire family had just $96.2 million in assets under management, with HealthShares Diagnostics ( HHD) holding the most, at $32.7 million. That means the average assets under management for the remaining 18 funds comes to a paltry $3.5 million.