Original: According to the accounts, Niobe boasted of her superiority to Leto because the nymph only had two children, the twins Apollo and Artemis, while Niobe had fourteen children (the Niobids), seven male and seven female.
Simplified: According to the Greek myth, Niobe boasted of her superiority to Leto because the goddess only had two children, the twins Apollo and Artemis, while Niobe had fourteen children (the Niobids), seven male and seven female.