I'm a UK visitor and it's the norm for us to visit both WDW and Universal when heading to the states, so I've never held a strong preference over either.
I also frequent both boards
Technologically, the Universal parks are far superior. The rides have a real wow factor and it feels more modern than Disney. However, they lack the tradition of Disney in my view
although neither is necessarily a bad thing. Universal is "wow" to me, and Disney is "magic".
The food at both resorts is good - although I've never had a bad meal at Universal, while I've had several at WDW (although in fairness - I usually do 3-4 days universal plus 10-13 days at WDW each trip, so statistically more likely to get a poor meal).
Planning wise - WDW takes months for a family of six, booking ADRS and FP etc - at UO you get the express pass if you stay on site and most restaurants are walk ups so it's a far more chilled out trip. It's a lot less stressful and with EP I've never felt the need to arrive an hour before the gates open! You can have a leisurely breakfast without needing to rush. Conversely, some people would legitimately argue that UO aren't working on a level playing field, as you have to effectively buy your way through their FP system.
Transport wise - the parks are walkable or boatable which I love, and I dislike the buses at WDW at times, but when they do work, they're great.
As a UK visitor UO works out cheaper than an on site deluxe WDW trip, but that depends on where you'd usually stay. I also agree that the higher end UO resorts beat WDW hands down - portofino bay is stunning!
Age wise I would say your kids are a great age for either resort, but I'm sure they'd have a blast at UO, even more so if they're tall and enjoy thrill rides. I'd do it in a heartbeat!