Quoting Supafly★:" I would do what you're planning, drive and come back. And I would take both kids. He's 4 years old, not ... [snip!] ... campground is an awesome place for a 4 year old. If it's 45 minutes altogether then it's right around the corner basically. "
Quoting dream:" just drive over for the day, both days, with both kids (unless the older one wants to stay overnight without you). it's not that long of a drive and then you don't have as much packing either."