Does willow smith have a brother?

yes! she has two, one is her half brother who is called Willard Christopher Smith III, i'm not sure is age but he is will smith's first son from his first marriage to Sheree Zampino who he later divorced. he later got married to jada pinket and they had a son called jaden smith who is now 12 (he starred in the remake of the karate kid along side Jackie chan) 2 yrs after having jaden they had another child who you have already stated is wilow smith aged 10