Climbing up our legs

Our new little kittens Rocky and Gabby think out legs are tree trunks. We will be sitting at the table or standing at the counter or something and all of a sudden one or both will land half way up our legs and proceed to try and climb the rest of the way. Needless to say it can be a little painfull.
Is there a gentle but firm way to stop them from doing this. They are still so young and we dont want to use any scare tactics. Thanks

It takes some time, but what works for me is to scruff them and put them about a foot away from you and walk away. As I pick them up I tell them NO. It takes ahwile, but they usually get the hint.

Sandie thanks I will try that.