Complex sentence: Research suggests that the alveolar trill is acquired and developed in between the ages of 3.0 and 6.6 years of age, some children acquire an adult-like trill within this period and some fail to properly acquire the trill.
Split into simpler sentences: Research suggests that the alveolar trill is acquired and developed in between the ages of three and six years of age. Some children acquire an adult-like trill within this period and some fail to properly acquire the trill.