Hiya Stefhany!
Welcome to planDisney! Many people don't know that the
Bibbidi Bobbidi Boutique at Magic Kingdom Park has packages for everyone including young knights. There is The Knight Package which includes hairstyling, a sword, a shield, and confetti for a pretty great price. There is also the Deluxe Knight Package which has a whole costume, hairstyle, sword, and shield. These packages are not guaranteed to be available as I have seen the Deluxe costume packages for even the princess dresses have limited availability. I would speak to the Fairy Godmother's Apprentices as soon as you arrive to figure out what is available. Maybe he can peruse the selection available before deciding on which package he wants to choose.
If your little boy just wants the sword and shield they can be purchased separately at
Sir Mickey's nearby. I found a great sword for my son here and a good selection to choose from. (Don't worry, they were not very hard.) You can also be sprinkled with some pixie dust at this location as well! Another location for that pixie dust is
Harmony Barber Shop. Both of these locations do not need an appointment for this special sprinkle and it is done at no cost. Just speak with the Cast Members and wait a bit for a little magic.
I hope your trip proves to be magical!
Happy Planning!
-Nimmy