The song is about dinosaurs, T-Rex, and how many there are.
T-rex is a dinosaur who has a number: one. There are three more in the world: two and three.
This is a nursery rhyme that has been passed through generations of children. It can be sung in many different languages.
Dinosaurs T-Rex Number Song | Nursery Rhymes & Kids Songs
The dinosaurs are coming out to play, the dinosaurs are coming out to play, the dinosaurs are coming out to play today!
The T-Rex is one, the Pterodactyls two, the Triceratops three and four. The Velociraptors five, six and seven and eight. The Stegosaurus nine and ten, eleven and twelve.
A brontosaurus thirteen and fourteen we will find today!
Souce: Cocomelon – Nursery Rhymes