[code]You're not meant to socialize with people at the event so knowing anybody there is irrelevant. You're meant to commandeer a corner for you and the toddler and keep him/her entertained with stories, coloring, toys, etc. Let the parents show the kid off, let the kid eat, and then let the kid fall asleep with their head in your lap and a napkin over them as a blanket.
This, except bring a blanket.
It's rude to try and cancel this late after you agreed to it. You'll be fine.