Do the visuomanual modality and the structure of the sequence of numbers in sign language have an impact on the development of counting and its use by deaf children? The sequence of number signs in Belgian French Sign Language follows a base-5 rule while the number sequence in oral French follows a base-10 rule. The accuracy and use of sequence number string were investigated in hearing children varying in age from 3 years 4 months to 5 years 8 months and in deaf children varying in age from 4 years to 6 years 2 months. Three tasks were used: abstract counting, object counting, and creation of sets of a given cardinality. Deaf children exhibited age-related lags in their knowledge of the number sequence; they made different errors from those of hearing children, reflecting the rule-bound nature of sign language. Remarkably, their performance in object counting and creating sets of given cardinality was similar to that of hearing children who had a longer sequence number string, indicating a better use of counting than predicted by their knowledge of the linguistic sequence of numbers.