Upvote:5
You will be fine.
What types of documents are accepted for entry into the United States via land and sea?
...
U.S. and Canadian citizen children under the age of 16 (or under 19, if traveling with a school, religious group, or other youth group) need only present a birth certificate or other proof of citizenship. The birth certificate can be original, photocopy, or certified copy.
A consular report of birth abroad is not a birth certificate, but it is definitely "other proof of citizenship."
Source: https://www.cbp.gov/travel/us-citizens/western-hemisphere-travel-initiative