Natural phonology puts forward that children simplify words in their utterances through strategies known as Phonological Processes (PP). According to this theory, phonological development consists of the gradual fading of PP. Evidence suggests the existence of numerous and diverse PP between 3 and 4 years of age; however, no exact description of this age period is available yet. In Chile, very few phonological development studies consider this theory. In addition, gender influences have been scarcely explored. Therefore, the following objectives were proposed: a) to describe phonological development in 3-4-year-old children by considering their use of PP; and b) to establish gender influences on this development. A sample of 180 participants was organized into two different age groups: a 3-year-old group (n 90; 42 girls and 48 boys) and a 4-year-old group (n 90; 45 girls and 45 boys). Both groups were tested with TEPROSIF-R to identify phonological processes. It was found that 3 year olds use significantly more PP than 4 year olds. Structural PP was more frequent in both groups. Regarding gender, no influence was found for phonological development. Findings suggest that girls and boys in this age period focus more on the acquisition of the structure of words, rather than on phonological oppositions.