Get him or her a cartoon cake which he likes the most
Theme party would be great
Make it theme based party!
Like everyone should dress according to a particular them, like Children for instance
Dress up your kid differently and decorate your home with balloons, you can also use customised transparent balloons for that and order some good food. You can do small pooja at home in the morning and in the evening you can also do online party with your friends and family at the time of cake cutting.