Usually, the birthday cake is toward the end of the party.
You don't have to chat a lot with parents, they will chat with each other. Just make sure you greeted everyone, and if someone is left out, you may want to chat a little with them. They understand that you have to take care of lots of things, don't worry.
If you give out birthday treats (favorites), make sure you prepare more than enough, someone may show up unannounced, or some kids bring their siblings. It is a good idea to give these out as they leave the party.
Most of the party we went to, the gifts are opened after the party is over. You do it when you got back to you home.
Have fun!