Simplify the following text for a Grade 3 native English-speaking person.
Original: They are capable of running rapidly in brief sprints up to 20 kilometres per hour ( 12.4 mph ) , diving up to 4.5 metres ( 15 ft ) , and climbing trees proficiently when young through use of their strong claws .
Simplified: They can run up to 20 kilometers per hour ( 12.4 mph ) , dive up to 4.5 metres ( 15 ft ) at top speed for short periods of time . When they are young , they climb trees with their strong claws .