I'm not sure about the exact ages of when you should or shouldn't pick up crying children, but I agree with your post prettybomb, in so far as giving positive feedback to any negative attention seeking, isn't really a good idea for either the parent or child.  It's awful to see parents literally being bullied by their children. It  seems that in some ways the adult thinks that they are soothing and comforting  their baby, when infact they maybe simply compounding the situation. 

I must add that I am not in anyway, saying that children do not deserve cuddles, love, compassion and the like, merely that it needs to be the adult in control of the child/parent relationship.  Easier said than done!!!!!!!