Bilingual speakers are confronted with a unique challenge when learning language as they must learn to express the same concept in two separate languages. Here, we examine whether learning number words in one language (i.e., L1) facilitates the acquisition of analogous number words in a second language (i.e., L2) or whether extensive experience and familiarity with numbers within the second language is required to learn words in L2. To do so, we tested 68 bilinguals speakers between the ages of 2 and 4 years and show that conceptual knowledge of numbers in L1 reliably predicted children’s conceptual knowledge of numbers in L2, suggesting that knowledge transferred from one language to the other. The effect, however, was limited to two developmental transitions: one-knower to two-knower and subset knower to CP-knower. Familiarity with L2 numbers as well as age were also significant predictors of children’s conceptual understanding of numbers.