We like this sort of party and did one for ds when he was seven. Massive success.
We built it round t-shirt painting as the children were older, but they also loved musical chairs, a Pinata, pin the tail on the donkey and pass the parcel.
We also did Kim's Game but again that's a bit old for four year olds.
We decorated madly (cotton reusable bunting seems expensive at the time, but it looks so lovely and can be used for family parties forever), loads of balloons, I had a similar marathon/useless dh experience myself, although he came into his own on bar duty later.
For four year olds, definitely musical bumps, TWO pass the parcels as fennel says, Sleeping Lions perfect in the run up for tea, if the hall is big enough you can do What's the Time Mr Wolf and Fox and Geese too.
A big dressing up box might be fun, and singing games - they all still love The Farmer's in His Den and the Hokey Cokey at this age