You probably gleaned from the site that Children's Parties are a big part of what I do. I love giving Kid's a party to remember and a big part of that is appropriate games to play.
The reason that I don't take party bookings for kids younger than 4 is that at a 3-year-olds party they aren't really ready for any kind of guided activity yet, and parties for this age group are really more of a get together for parents and friends. I am happy to book these as a Disco with a little time set aside to make a fuss of the kids, but it is a different kettle of fish from 4-year-olds onwards.
Once children are turning 4 and onwards (reception class at School) then their own social world is developing and the party is really for them and their friends, and I really want to make sure they have the best time ever.
This means Dancing and Prizes, but most importantly GAMES!
Now you will forgive me for feeling like I am being scientific about it; but I try to arrange the games for maximum enjoyment and participation among all the kids.
I have a large variety of games, both themed to various parties (Princesses and Pirates, Spooky Halloween, Beach, Jungle, Popstars) as well as 'generic' non-themed DJ Dan Party Games. Some of these games involve bulky props (inflatable or wooden) which I bring with me. Within these games I also know which are appropriate for different age groups (8-year olds are too big for musical bumps, 6-year old's are too little to wrap Mummy in 'bandages' et cetera). I can divide some of these down easily enough into games suitable for 4-6, games for 7-8, and games for 9-11 year olds. There are some games which overlap, but these are distinct enough stages of child development that I know which games are sensible to bring with me dependent on the age of the Birthday Kid.
Stepping up to children of Secondary School age, they aren't going to want party games. In order to have an icebreaker with me I may bring a Limbo set (also used at most other parties - it is a great game) and possibly something else secret! But generally Teenage Parties are about the Music, the Lights, and DANCING!