Engineering internships: diverisfy or stay with one company multiple summers?

My S23 was fortunate to have an internship after his freshman year of college. He has declared Civil Engineering as his major, and he says he is 7/10 confident that it’s the right fit for him. The company he worked for invited him to come back next summer which is great. They have an office in our small town which was convenient, and they treated him very well - good pay rate, generous mileage reimbursement, and a small tuition scholarship. He does not want to live here after he graduates, but they do have other offices throughout our state. I am wondering if the general advice would be to stick with one company for multiple summers, or to try to secure a position with a different company? What are the pros and cons?

My D is doing a three term coop with the same company. The big pro is that the higher almost all their coop students after graduation so good job security.

That said, she is looking to work for a different company during her off summer so she has something else to compare to.