Massaging and gimnastics usually helps. Be sure the body parts are warm. Perhaps by warming up by IR-warming lamps. The warmths from them goes deeper than the usual warmt.
And massage and exercise these legs several times a day... Pretend you are playing with the kitten... Sing, laugh, talk merrily...
With humans this bowed legs, the so called rachitis or English disease, is caused by lack of vitamine D. As I know, cats do produce themselves their vitamine D, but some extra may be useful? Ask the vet when you visit for advices. Not least, so you are sure the dosages arent too high.
Yes, act now to straighten the legs. It’s a tendon problem that is usually the result of being squished in the uterus, but can be straightened while the kitten is young and bones and tendons are still somewhat soft and malleable. Be sure to massage and warm up the limbs before wrapping.