Thanks gayleggg, I guess it was just basic and primitive impulse of jealousy.
What I was afraid was some immature issues. I know that kids are selfish, and that is the way they need to go through. Guess everything will find its place. I don't have kids so I don't have this tolerance managed yet.
Your friends grandchildren are raised in different manner so maybe it is too hard to show your own way of behaving to them, so you maybe stay reserved and save your nerves