Many families first notice 16p13.11 microdeletion syndrome in early childhood when developmental milestones arrive later than expected, such as delayed sitting, walking, or first words, or when a pediatrician flags low muscle tone and feeding difficulties in infancy. Some children are evaluated after learning or attention challenges surface in preschool or primary school, or when seizures, unusual head size (either smaller or larger than average), or subtle facial features prompt genetic testing. In other cases, the first signs of 16p13.11 microdeletion syndrome appear prenatally through findings like growth differences on ultrasound, leading to chromosomal microarray testing that confirms the diagnosis.