I'd think suburban kids who don't know farming terminology would choose just the most obvious, descriptive, easy label for something they didn't know; if they were to label a tramline (as opposed to just saying - assuming the crops are fairly mature - "Let's follow this path."), they'd likely give it a name that comes from their own interpretation of what the tramline must be.
So, whether there are tyre marks or not, they might call one of the tramlines a tyre path, tyre channel, tyre trail, tyre line, wheel furrow, driving furrow. I'd expect the name they give tramlines to be somewhat awkward, quickly chosen, and chosen for its ease of use in conversation.
Also, in the country where I live communities with trams aren't that common nowadays (it's mostly big cities that have them). Not sure if the kids in your story have grown up in a town with trams? If not, they'd possibly be more likely to think of rail lines, than tramlines (in case you do have one of the kids explaining the lines looking like tramlines). A few thoughts - it's 5am here, so they may not be cogent thoughts.
edit to add: almost any teen should know what a tractor is, and might connect tire trails in a field to tractors (rather than, say, threshers or sprayers). I'd think something like tractor trail, or tractor path would come right to mind, especially if the crops are even moderately mature (when just plowed a field is a field, and the tramlines aren't that distinguishable). Okay, bedtime, not rambling time. I hope someone here can help, HB! CC