*Time:* Poster Session B (March 20th Friday 12:10 – 2PM) Join us for a Zoom meeting now! https://umass-amherst.zoom.us/j/8973659528 Jihyun Hwang will be available during this time. I would be happy to give a brief presentation or answer any questions. If you cannot attend our virtual presentation and would like to know more, we can talk via OSF comments (click the icon at top right corner) or email (jihyunhwang@umass.edu). *Abstract:* Complex numerals are constructed by recursive Merge operations between Digits (one to nine) and Multipliers. Our hypothesis that children understand the syntactic structure of complex numerals for acquiring entire number concepts was addressed by devising a number word comparison task. Children (4-6 yrs) chose the larger number after hearing two single digits or complex numerals. We found that (1) children correctly compared complex numerals beyond their counting range; (2) the structure of complex numerals, not non-numerical constituents, disrupted children’s ability to compare the targeted digits. These results support that children understand the compositionality of complex numerals prior to knowing their meaning. *Contact information:* If you have further questions about our work or are interested in collaborating with us, you can contact us, Dr. Joonkoo Park (joonkoo@umass.edu) or Jihyun Hwang (jihyunhwang@umass.edu).