I would say stopping with your pup for 5 to 10 seconds on a walk is more of a pause than a break. haha
I often just sit down and hang out with a pup who wants to take a break and observe their environment in the middle of a walk.
Its still good exposure for the pup, IMO.
They might be picking up an interesting or new smell as it wafts past them through the air. Maybe they're just quietly observing the scenery and thinking about their surroundings. It's good stuff for puppy brains.
One of my favorite ways to socialize or expose puppies it to take them new places and hang out somewhere out of the way and people watch. We'll also explore the area a bit, as they're comfortable, but I let them kind of lead the way on that. My general approach is just that we observe the environment and explore at the pup's pace, whatever that may be.
Really, the only time I expect my dogs to be on the move is when we're working heeling patterns (and I've never met a dog who was ready for heeling patterns as a little puppy hahaha). They don't get to decide to stop mid-heel when we're training. But for normal walks, we can stop and start again as much as they want and I don't care. Walks are more about enrichment for my dogs because, honestly, neither of my dogs' exercise needs can be met by a walk each day. They're not over the top active but a walk doesn't exactly cut it either.
So, if I were you (assuming its not about to storm or you're not going to die of heat exposure or at-risk of some other tragedy), I'd probably just sit down and let the pup take in his environment for a while.