She may just be slower developing and if she is the heaviest kitten that would not be unusual.
But there are problems kittens can have from their mom having a viral infection while she was carrying them. You can read about 'spastic' cats here to see if that is what you are seeing.
http://www.messybeast.com/disabled.htm
So she just might be a day or two behind her siblings but if she continues to have mobility issues she may be a special needs kitty.
Cats can have hip socket issues too. When she gets a little older if her legs are still an issue you might want your vet to check her out for you.
Hope this helps you!
Edited by NHolmes on November 6 2005 at 10:33 AM
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