I don't think that it is surprising that children do the "no-with-giggles" right away. It is a learned behavior. As far as teaching them to say yes to tickles o

I don't think that it is surprising that children do the "no-with-giggles" right away. It is a learned behavior. As far as teaching them to say yes to tickles or not... I don't think it will have any bearing on language development. Some may benefit from knowing that some people will not adhere to your "no" command.