We had a 'traditional party games party' for my son on Saturday (his 5th), and also last year - the children loved it. I would say: Keep things very simple - many of these children will not have played traditional party games (much) before, so aim low, and explain the games carefully - don't take anything for granted. Don't worry about winners, or prizes, they don't care at this age. Don't eliminate people when playing musical bumps/statues, etc. - it's not necessary. Some of the best 'hits' for us have been:
Copycat - simplified Simon Says. You say - 'hop on one leg, jump up and down, put your hands on your head' ... etc. Then 'Copycat!', at which point they have to sit down and fold their arms and cross their legs. (I know it sounds banal, but they love it!)
Hunting/searching games - Last year we put easy-thread beads mixed up in buckets round the room. Each child had a string with a single bead, and they had to find the other ten matching beads, and thread them! They loved it. This year we scattered two colours of wool (c. 4" lengths) around the garden, divided them into two teams, and they had to collect the right bits of wool, and bring it to the team leader, who knotted it together.
Tell a story and get them to make animal noises.
We borrowed a parachute, and played parachute games in the garden. (4 may be a bit young for this, unless you have some bigger ones there too?)
Last year we did DIY icecream sundaes - loads of chopped fruit, cream, ice cream, sweets, sauces, and let them run riot - great fun!
Try some simple singing games - In and out the Dusty Bluebells is my favourite (nostalgia!)
If you are doing pass the parcel for 12 or so, I'd recommend having two parcels, as it gets fairly tedious at that age if there are endless layers.
I've got loads more ideas ... If you've managed to read this far, let me know!