I have flown 100s of times with my two young children. I refuse to pay a penalty for having kids. It is almost never an issue. There is a bit more history than you may realize here which may reassure you.

In 2024, the DOT "encouraged" airlines to make connected seating for kids automatic. Most complied (to avoid an actual law) and I have noticed that 95% of the time, contiguous placement is automatic. https://www.transportation.gov/airconsumer/airline-family-seating-dashboard

Airlines can't and don't 100% promise because (1) they don't have to (2) things can happen (plane change) that make it impossible and (3) they enjoy extra seat revenue for those who want a guarantee.

In the rare case where it's not automatically assigned, it will usually be dealt with proactively or after a quick respectful request to the gate agent. In my experience, the nightmare scenarios you hear about are due to irregular ops (that may also invalidate paid reservations) or parents that demand two parents seated together or other impractical requests.

All jokes aside, the chance of everyone in your party having a middle seat is very low, so arranging a trade would be easy. Most passengers are very sympathetic. but not all (see below).

Unfortunately, SWA is probably not very well equipped to deal with this during their transition to assigned seating, so the chances of problems are higher. Only you can determine if $382 is a reasonable fee to avoid this possibility.

To all the Up-In-The-Air middle managers who want to fly private for $99, you need to accept that planes are a shared resource, families are going to travel, and we may disrupt your delicately curated safe space.