Ollie and his dad were travelling along the A350 in Wiltshire, when they collided with a Ford Mondeo, on October 28.
Firefighters from Trowbridge Station scrambled to the scene which they described as "horrific".
Marek Adamiak, 42, and Radek De, 28, were pronounced dead, despite paramedics best efforts.
Thanking them for saving his life, Ollie drew an picture of the crash, and wrote: "To the fire fighters men and ladies. Thanks for helping me and my daddy on Sunday 28 of October 2018."
After the accident, the firefighters tweeted: "No 7yo should have to see what this tot saw".
Ollie was later invited to the station to learn about how the firefighters prepare to head out on jobs.
On Twitter, the firefighters wrote: "Remember Ollie? Unfortunately he witnessed something terrible.
"He sent us the attached picture so we wrote back and invited him to the station for a visit. We wanted to check the little man was ok."
Ollie's drawing left dozens on social media emotional.
Diana wrote: "Aaw that is great, hope Ollie is able to feel a bit better after his visit- I’m sure he will have had a great time."
Chrissy added: "Awww Bless him…Hope Ollie will be ok."
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