Hi Dinah!
Welcome to the Moms Panel and thanks for your question!
While you can always check the Calendar to see when fireworks are scheduled for your visit to
Magic Kingdom and
Epcot, it looks like 9pm for Illuminations at Epcot and 10pm for Wishes at Magic Kingdom all throughout your visit!
California Grill has a fantastic view of the Wishes fireworks, with the music played along with it. It's also a great restaurant for a delicious dinner. It makes for a great way to experience the Wishes fireworks from outside of Magic Kingdom. Another magical way to see the Wishes fireworks that your four year old might really enjoy is by participating in a Pirate and Pals Fireworks Voyage, you can see information
here.
Illuminations is also a fireworks show worth seeing over at Epcot. (Disney really makes their fireworks shows spectacular!) However, you will need admission for the park if you wish to dine inside.
Hope this helps! Come back to the Moms Panel if you have more questions!
Have a magical vacation!!