Twin Development Differences
The short answer
It is completely normal and expected for twins to develop at different rates, even identical twins. Each child is an individual with their own developmental timeline, temperament, and strengths. One twin may walk or talk earlier, be more socially outgoing, or reach milestones in a different order. These differences are rarely a cause for concern unless one twin is significantly behind established developmental milestones for their age.
By Age
What to expect by age
Even in the first weeks, twins may differ in alertness, feeding patterns, and sleep schedules. Premature twins (common in multiple births) may have adjusted ages that differ from their actual birth date. Developmental comparisons should be based on adjusted age if born before 37 weeks.
One twin may roll over, reach for toys, or babble before the other. These small differences are normal variation. If both twins are within the normal range for their adjusted age, different timing is not a concern.
Differences in motor development (sitting, crawling, pulling to stand) may become more noticeable. One twin may be more physically active while the other is more verbal. Each child should be evaluated against standard milestones, not against their sibling.
Walking and talking timelines can differ significantly between twins. One twin speaking in sentences while the other uses few words is not uncommon. "Twin language" (cryptophasia) may develop but usually resolves with increased exposure to adult speech. Monitor each child individually against age-appropriate milestones.
What Should You Do?
When to take action
- Your twins reach the same milestones days, weeks, or even a couple of months apart
- One twin is more physically advanced while the other is more verbal or socially advanced
- Your twins have different temperaments — one is outgoing while the other is cautious
- Small differences in size, weight, or head circumference between twins at well-child visits
- One twin is consistently missing milestones that the other has achieved and falls outside the normal range for their adjusted age
- The gap between your twins' development seems to be widening over time rather than narrowing
- One twin shows signs of developmental delay — such as no babbling by 12 months, no words by 16 months, or no walking by 18 months — even if the other twin is on track
- One twin shows sudden loss of previously acquired skills such as language, social engagement, or motor abilities
- One twin has significant feeding difficulties, failure to gain weight, or signs of a neurological problem such as persistent asymmetric movement
Sources
Related Resources
Related Behavior Concerns
Sibling Rivalry in Toddlers
Sibling rivalry is a completely normal part of child development and is nearly universal in families with more than one child. Toddlers are naturally egocentric and have limited ability to share, take turns, or manage frustration — all of which fuel sibling conflict. While it can be exhausting for parents, most sibling rivalry decreases as children develop better language and emotional regulation skills.
Aggressive Play vs Normal Play
Rough-and-tumble play — wrestling, chasing, play-fighting, and superhero battles — is a normal and important part of child development, particularly for toddlers and preschoolers. It helps children develop physical coordination, social skills, self-regulation, and an understanding of boundaries. The key distinction between normal rough play and concerning aggression is whether both children are having fun, there is turn-taking in roles, and no one is intentionally trying to hurt the other.
My Toddler Is Aggressive Toward Pets
Toddlers being rough with pets is extremely common and almost never reflects true aggression or cruelty. Young children lack the motor control to be consistently gentle and do not yet understand that animals feel pain the way they do. With patient, consistent teaching about gentle touch and close supervision, most toddlers learn to interact safely with pets by age 3-4.
My Baby Doesn't Seem Attached to Anyone
By 7-9 months, most babies show clear preferences for their primary caregivers and some wariness of unfamiliar people. If your baby seems equally comfortable with everyone and shows no distress when separated from caregivers, it may simply reflect an easy-going temperament. However, if combined with other social differences, it can occasionally warrant further discussion with your pediatrician.
Attachment Parenting Burnout
Attachment parenting principles (responsive feeding, babywearing, co-sleeping) can foster strong parent-child bonds, but the all-encompassing nature of the approach can lead to parental exhaustion and burnout, particularly for the primary caregiver. Research shows that secure attachment comes from being consistently responsive to your child — it does not require 24/7 physical proximity, exclusive breastfeeding, or co-sleeping. A burned-out, resentful parent is less able to provide the emotional responsiveness that is at the true heart of secure attachment.
Baby Arching Back and Crying During Feeding
A baby who arches their back and cries during feeding is often showing signs of discomfort. The most common cause is gastroesophageal reflux (GER) - stomach acid flowing back into the esophagus causes a burning sensation, and the baby arches to try to relieve it. Other causes include an improper latch (breastfeeding), a bottle nipple with too fast or too slow a flow, ear infection pain worsened by swallowing, oral thrush, or being overstimulated. If this is happening regularly, discuss it with your pediatrician.