Biscuit decorating? Little pots of icing and sprinkles plus a packet of gingerbread men or rich tea keep my dcs busy for a while. You could have some paper plates and stickers to decorate for another activity.
I just hosted a party for my dd who turned 3 & 6 of her friends aged between 3 to 6 years old so same as your age bracket.
I organised 2 structured party games (pass the parcel & pin the tail) which they enjoyed but they preferred free play instead. Musical statues which turned into a mini disco so no winners or losers!
I arranged all the furniture against the main wall & put the table adjacent to it so there was a large open space for kids to play. In one corner I set up a mat with toys & the coffee table became the craft table with an activity to start with while waiting for all the guests to arrive.