I had DS's 1st birthday recently, from 11-1, so I treated it as a morning tea and not a lunch thing. I was trying to keep it super-simple for myself and didn't even do different food and drink for adults and children.
Ham, and cheese & tomato sandwiches
Drink - 300ml bottled water, and juice cartons.
That's it! Almost but not quite all the food was eaten, I saw all the adults nibble away, and if anyone was unhappy they didn't tell me about it!!
You could do savoury mini muffins instead of sausage rolls - so then everything can be eaten cold. Fairy bread I made fresh on the day. Honey joys can be made several days ahead and stored in air-tight container. Mum brought the plate of sandwiches. Savoury mini-muffins (or sausage rolls) can be made weeks in advance and frozen, thaw on the day and serve. Birthday cake I made weeks beforer, froze, and then decorated the night before.
Hope that helps