Just had my daughter's 4th birthday party and being 36 weeks pregnant with number 3, it was scaled down somewhat food wise from other years. My tip would be to have a bigger quantity of a smaller selection of foods (easier to make bulk amounts than lots of different bits and pieces).
We didn't do heaps in thermie for a change-fairy bread (with bought bread-shock horror!!), a big fruit platter, and lots of sausage rolls (homemade filling in thermie but with bought butter puff pastry). For an afternoon tea it was sufficient and we still had lots of leftovers somehow. Also did the cake-love the EDC chocolate cake (a x4 batch to make the train) and some great thermie choc icing from a recipe off someone's blog-been meaning to upload it, it is insanely good!).
Honey crackles are a good one. The recipe off here is great, so easy and you can do it a day or two ahead of time. Choose other things like it that you can prepare before the day as that sounds like when you'll have more time...and don't feel like it needs to be a feast. Much better to relax and enjoy the birthday celebrations yourself too.