Hi, Abby here, with tips based on years of experience working exclusively kid's shows.
Tip 1: Hire a magician only after most of your audience reaches age 3. Most one and two year olds are not developmentally ready to enjoy a magician -- even a silly one. I enjoy seeing infants at parties, as long as you're aware that they seldom get much out of seeing a performer.
Tip 2: Hire someone who brings a microphone system. Good magicians generate enough laughter and hubbub that a microphone is usually needed.
Tip 3: Here are some good questions to ask the magicians who you are interviewing:
How many years of experience does the magician have?
Will this magician avoid language and stunts that you wouldn't want children to mimic (fire, sharp objects)?
What percent of the magician's parties have been children's parties?
What's the age range that responds well to this particular magic show?
Are you reassured by the magician's professionalism?
Other than the magic show, what else do I get? (Balloon sculptures, party favors, birthday present?)
Here's how to optimize the setup when hosting a magician.
1) Larger groups laugh more. For birthdays I recommend having at least 15 children present. Groups of 30 or so laugh even louder. Of course, smaller groups allow more time for fancy balloon sculptures or for balloon seconds, so there are advantages with small groups also.
2) It's helpful to time the magician's performance for latecomers. Picture it: a family arrives late. Someone blurts, "you missed the magician!" This disappoints a child. Start your magic show at least 30 to 60 minutes after your party starts.
3) Even if your party is outside, put the magician's performance indoors. Based on over a decade working as a magician with sun glare, heatstroke, rain, wind, bees, mud, grass stains, dust, dog doo, and children running into the street, it usually goes better indoors.
4) Sitting on the floor gives children a better view than sitting in rows of chairs.
5) Clearing the room of toys beforehand reduces tripping and distractions.
6) Are there toys remaining in the room? Hide them. Out-of-reach toys may distract a young child to tears.
7) For grownups planning to chat rather than watch the show, provide a separate room. It's hard to compete with a magician's P.A. system.
8) Toddlers will toddle and need to be individually supervised for safety.
9) Decaffeinate. I've worked tea parties where they served full-caffeine tea and it showed.
10) As the magician departs, use an upcoming activity such as cake, pizza, or games. This reduces disappointment over the magician leaving.
I hope this advice is helpful.
Best, Abby London, The Children's Magician