Saw this on TV years ago so I think it was B&W or that could just have been our telly. British film from 50’s / 60’s about two boys running away from a city (possibly London) by stowing away on a removals van.
An important scene is when the van stops at one point and removal men check the load. They are concerned that a potted plant might suffer on the journey. One of the men checks it and says if feels well watered (implying the boys have been using it as a toilet!).
Thought I’d found it myself but was wrong so I can say it’s not ‘On the Run’ (1968)