As an experienced breeder I have to tell you that feeding fry that Walmart stuff or any other pre-made food is generally the first step to losing your spawn. Betta fry do not usually eat something that is not moving. BBS must not be overfed or it will cause swim bladder and parasites, and bacteria and kill the fry. The best thing you can feed your fry until they are old enough to eat normal food, namely bloodworms, is microworms. The cultures are EASY to make. You can check Craigslist or put an ad on Craigslist or your local aquarium hobby forum for someone selling cultures. They typically only cost 5-10 bucks and you can keep them going forever. BBS are good but only if you feed them a little bit every couple of days.
I've never gotten swim bladder from microworms, but have from the BBS. Considering buying the frozen worm tablets from Petsmart. They aren't good for your fry, again fry like their food alive, but they are great for conditioning your breeding pairs.
I can give you more info if you like. I am currently setting up a halfmoon spawn.