Non-traditional places for the fireworks...
Behind the castle. You'll be able to experience the fireworks going off all around you. Bonus, if you watch in front of Beast's castle some of the fireworks look nice behind the castle and you might be able to find a photopass photographer who is set up and can get fireworks in the background of your picture.
On an attraction. Fireworks are great from Dumbo, sometimes the CMs will even keep the spinners going and let you stay on. SDMT, if you are riding this during the fireworks they go off all around you. If you plan this, I would try to time it so you see the beginning, then you can stay in Fantasyland and watch. Also BTMR, but the 5 year old may be too young for that.