Put "splayed legs," in the search box and you should have several suggestions/ information pop up. People generally make a little hobble out of bandaids for the legs so they can't spread far apart. Do you have good footing in brooder? Slippery flooring like newspaper is hard for a chick to walk on, and makes it harder for them to control their legs.
Some people put down the vegetable bin mesh liners which give some grip for the chicks.