24 day old kitten now fully walking but sometimes doesn't move back legs

Sometimes they move their back legs but sometimes they pull forward like skis or like front wheel drive. They don't look limp or painful. They did just start walking a couple days ago and just now leaving the nest area. A different kitten also lays back very relaxed when i hold them on their back. I'm worried it's neurological because the parents were siblings. (I did not want this to happen of course but I wasn't able to get the mom spayed in time. The mom was also a stray I was trying to unofficially foster and theyre all going to the Humane Society soon because I trust people who would adopt through there more than I trust people at Walmart to take them home and spay/neuter etc for them)