That’s what war and siege does. People lose children a lot so they have more children.

This is what it means to live in Gaza:

0–14 years: 44.1% (male 415,746/female 394,195)

15–24 years: 21.3% (male 197,797/female 194,112)

25–54 years: 28.5% (male 256,103/female 267,285)

55–64 years: 3.5% (male 33,413/female 30,592)’

65 years and over: 2.6% (male 24,863/female 22,607) (2018 est.)

Edit: source https://en.m.wikipedia.org/wiki/Demographics_of_the_State_of_Palestine