Character mistake: Baymax, a healthcare robot, says that his programming includes a database of 10,000 symptoms of disease. Yet, he issues the warning, "After eating, wait one hour before swimming." That warning, often given by parents to their children, has no basis in medical fact. People who do not get cramps after eating will not develop cramps by going swimming after eating: http://www.snopes.com/oldwives/hourwait.asp.
Factual error: When Honey first meets Hiro, she is rolling a solid ball of Tungsten Carbide that is about 2-3' in diameter. Honey claims the ball is 400 lbs. Tungsten Carbide is very dense, around the density of gold, but much harder. The specific density is 0.54 lbs per cubic inch. If the sphere was only 2 feet in diameter - it would weigh approximately 3,619 lbs - or about 1.5 tons. If it was 3 feet in diameter it would weigh an astonishing 12,200 lbs - or just over 6 tons. Honey would not be able to roll it around on the floor as easily as she appears to do in the movie.
Continuity mistake: At the end, Baymax rocket-glove changes model. When Baymax puts his Rocket-glove at the thruster on the ship it has the original model seen earlier in the movie, however, when the ship exits the space through the portal and the glow shuts-down it has another model.