In my opinion, Chef Mickey's is a must during a WDW trip.
Walt Disney wanted you to take the monorail from the park into The Contemporary resort. He wanted you to be "wowed" by that unique experience (you can't take a monorail into a resort anywhere else on earth...remember that when you go!).
The food is excellent. The character interaction (without giving it away) is terrific.
I will recommend something to you: Consider dressing up the family nicely for the dinner (specially since it's your son's birthday). Just before you are seated, the CM's will take a professional photograph of your family in front of a Chef Mickey's background. During your meal, they will come around with the picture as an 8x10, magnet, key chain, etc. Tell them how wonderful the picture turned out. Say how you must buy the 8x10 but that you have to watch your expenses and you wish you could afford to buy everything. When you pay, tip the salesperson a couple dollars. I've done this three times and every time, they just gave me the whole package! It's already made up and and they just throw away the stuff you don't buy anyway!
We bought matching Disney outfits that we wore to dinner.
Good luck and enjoy!