We use the fine, self-adhesive1/4" wide white tape that comes on a roll. Tape the legs so they're no further than the width of the body (including down) apart and remove after two days if slightly splayed or three if worse. Is it all the chicks or one particular breed? We had a beautiful Dorking cockerel that produced too many chicks with splayed legs so we switched to our much more ordinary reserve cockerel and the problem disappeared.