Whooa there! I can totally understand your panic because the mere thought of entertaining a party full of tinies used to (still does!) bring me out in a cold sweat. But I've been round the block a few times with this now.
Rule one. They don't eat much. I promise you, no matter how much trouble you go to you will either throw it away or end up eating most of it yourselves for the next umpty two weeks.
Rule two. Keep it minimal and simple.
Rule three. Buy yourself a big bottle of wine.
The easiest thing to do is to get some of those party boxes for food. Children love to have their own box and it saves you worrying about plates etc. Been there done that. Hassle. Party Pieces do them or places that sell party stuff.
Provide a bottle of water each. One with a sports type top. Buy lots of water cos little ones get thirsty. No sticky squash which some might not be able to have anyway and which gets knocked over.
Come up with about 5 things to put in each box. Ie A small yogurt and plastic spoon. A cheese string. A homemade sandwich. Some crisps. Grapes or carrot sticks maybe. A fairy cake. Chocolate fingers. A pretty napkin. Maybe a hat to wear if you want to jazz things up a bit.
Make up a box for everyone you've asked. If some don't arrive at least you're covered and because the food is minimal you won't have over-catered massively. (grrr at no replies from some. V rude but it happens)
Birthday cake of course for the party bags. If you have a lot coming and you don't think the cake will stretch round everyone, either buy or make a simple sponge cake and bump it up with that. I've done that before and no-one notices once it's cut up.
Oh and the wine is for you when it's all done and dusted