We did it with out 13month old ds. We had Michael and he was good. He plastered ds with stickers as a distraction and gave my mom bubbles to blow as well. My ds was a champ and sat through it to get his "first haircut" ears. He did not get any glitter paint put in his hair.
We did have to wait for about 30 minutes to get in. There are no appointments - it's first come, first serve.
What I would suggest to you is that you bring something to distract your son while he is getting his haircut in the off chance that there are no bubbles or stickers. Don't expect anything except for a decent hair cut and the enjoyment of the memory that your sons first haircut was in the Magic Kingdom. If you go in expecting more, you may be disappointed if something "neat" that happened to someone else didn't happen for your son.