The prefinish on these floors is supremely tough. Some of these finishes contain fine silicon dioxide particles to prevent wear-through. I would believe that the face of the flooring is waterproof and darn near bulletproof. Bonding a manually applied finish onto this would be weak IMO.
I don't think it would make any difference even with the most optimistic assumption that thinned polyurethane might penetrate the seams to some degree. What spells the difference with wood, and laminate products in particular, is whether a given area is wetted before it has chance to dry from the last exposure. There is no such thing as dry rot!
It's gotta be wet. I'd think that the random nature of kid & pet accidents wouldn't lead to a big problem for you. Just keep an eye on regular exposure to moisture; eg, around the pets' water dish. I think you'll be more than okay without the Minnwax Polyurethane ... and honestly ... I think you'll be ahead of the game for avoiding it.