My second baby was just born last month. As my first one is about 5 years old and is studying in kindergarten, you need to tell the teachers once your wife is pregnant. It is because to the big one, a new family member is a big impact/change to him/her. We need more time to explain to him and let him adopt the change. Since my wife laboured by scissored, I brought my son to see his little brother coming to this world and he felt very happy.
Even now if we ask her who sent her the gift, she still remembers it's from her little brother
But a gift itself is not enough. You (or your wife) need to devote more time to your 1st B, otherwise he might try to hit/bit/etc your 2nd B (when you are not watching.....)