I think the biggest thing is to just enjoy yourself! You are going to a fun event, try to relax and just go with the flow. How much have you been around any kids before? If these are the first kids that you will have ever really interacted with then that is going to make it a little more interesting. Get down to their level, let them set the pace, be friendly but not pushy, and don't fawn over their dad! Kids are possessive little monsters at times (said with love...) and excessive hand holding, being lovey dovey with their dad will probably not go down well. Biggest thing, have fun!! And honest! Do not put on an act as kids are normally pretty good at spotting fake from a mile away.
No matter who is president, I will live life with an open and loving heart, kindness, and tolerance of all good people. I will stand against racism, sexism, and all prejudices!