I always hire a village hall(we are rural), we always invite the whole class, it across the road from school so start fifteen minus after school,
we play lots of silly party games, (have several parcels going round at a time)
we have mini loop donuts hanging on string which they have to eat with their hands behind their backs,
followed by ducking for apples in a trug of water(washes the sugar off)
lots of silly games set up in advance,
sit them all down table full of party food, eat
musical chairs, musical statues , balloon games
mexican piñata over loaded(instead of party bags)
send them home by 5.45, out of hall by 6.30.
our hall cost about £20 for the afternoon, and we make the food, sandwiches, pizza, sausage rolls, buns, cakes, biscuits, fruit, crisps, fizzy water , fruit juice.
a sweets for the piñata (I make one, but you can buy them)
Find the nearest community hall near the school, and go from there.
I did the first party when my first child started at school, as a way of them getting to know their new class, and they request a version of it each year, we had a DJ party there last time for the older ones, mixing desks, and a break dance floor, a friend who is an expert break dance came along and gave lessons, they loved it.
doing your own thing in a hall is always far cheaper than hiring a venue.