We didn't expect anything serious to come out of the second Madagascar. We just wanted to do something with the kids that didn't entail sick Mommy moving. We were surprised, more than once.
The movie begins with young Alekei in an African Wildlife Preserve, clearly the treasured son of the pride's Alpha male. While his father is occupied fighting the Beta-lion (voiced by Alec Baldwin, looking very much the feline version of the actor) the toddling cub is lured off the reserve. His father tries to save him (and for a moment appears to be shot) and Alekei is washed away. Soon a rescued Alekei turns up in the Central Park Zoo, renamed "Alex," and we are back in the familiar territory of the original film.
A quick sequence takes us through what has brought our four heroes to Madagascar (a device some reviewers found annoying but I found fun) and soon, they take off in a fragile plane, only to be grounded on the continent proper. Soon Alex realizes that he has landed on his native ground, and he is reunited with his father and mother (and the film explicitly refers to Roots). Alex/Alekei finds what he has always been missing (though the performing King of New York has no survival skills necessary for the King of the Watering Hole). Marty finds that in the zebra herd, he doesn't stand out anymore. Gloria finds true love.
Alex/Alekei's forced removal from Africa and separation from his doting father and his renaming was hard for the Bloom family. Thankfully, however, it affirmed that Alex/Alekei had always been loved at home, and in the end, the adult Alex was who he was in a combination of nature (as a cub he was inclined to dancing) and nurture, in Africa and in the Central Park Zoo, by his beloved friends. Marty, too.
More conservative families may find objectionable a penguin's romance with a dancing hula girl, and the interspecies infatuation of a giraffe and a hippo. Of course, this is no less weird than the polymorphic perverse (in the Freudian sense) King Julian, who comes along for the ride.