Can he say the 'TR' sound?
Years ago when my mom had a passel of little kids and so did a neighbor they had an agreement that once a week one mom would take all of the kids for a few hours so each mom would get just a little time without constant kids. Well one of the other ladies' kids was a toddler who loved trucks, however he couldn't say the 'TR' sound but instead it came out as a 'F'. Keep in mind this was the late '60s/early '70s so there weren't really car seats and a kid would likely be standing up in the back seat around town shouting out the open window. My mom said she had never encountered so many trucks. That kid was shouting and pointing out the window at the top of his lungs, "Phuck, phuck, phuck!!!"