Bindi Irwin makes a promise to her brother Robert on his 18th birthday

Robert Irwin Turns 18: Sister Bindi, Mom Terri & More Send Him Heartfelt Birthday Wishes

Bindi Irwin Celebrates Brother Robert With "Stocked Fridge" as He's All Grown Up on 18th Birthday

Bindi Irwin Has 'Tears of Happiness' After Daughter Grace Sees Her First Christmas Tree