OK, we'll rule out VS as the first choice or any recommendation.
The US service from LGW would be via connection in CLT - Charlotte, North Carolina - a large hub for US and a great airport to clear customs and connect on to MCO. Much has been said about US and its transatlantic product - some of it not always a positive - more hit and miss - but you would fly on a A330-300, have a meal and snack and complimentary (non-alcoholic) beverages. In-seat AVOD and with a 4 abreast center section, good seating for the 4 of you together. Total travel time is almost 15 hours, with a 3 hour layover in CLT.
Thomson/Thomsonfly. Not familiar with their in-flight product but from the standpoint of traveling with 2 children, nonstop I assume from MAN, to a smaller and effecient airport you are familiar with, I'd strongly suggest you consider their service. Certainly your accessability to the Greater Orlando area is equally convenient at SFB with ground transportation options (shuttle service or car hire) and less congestion.
I doubt you'd be hugely disappointed with US so in fairness their service is worth considering if you're comfortable with the longer journey time and how you feel the chidren will manage on the trip.
I hope you can plan a visit to our beautiful beaches here in the Tampa Bay area. No oil except in a Petrol Station! Good Luck with your plans, and let us know what you decide.
watch what you want. you may get it.