This is the 1230th most frequent Dutch word.
allebei
"Both."
In this sentence, 'allebei' is used to collectively refer to two items that have been mentioned (both types of fruits).
Ik hou van beide soorten fruit; ik eet ze allebei graag.
I like both types of fruit; I enjoy eating both.
Here, 'allebei' emphasizes that both subjects (the boys) performed the same action together.
De jongens gingen allebei op een avontuurlijke reis.
The boys both went on an adventurous journey.
'Allebei' indicates that two people made the same choice regarding the dish at the restaurant.