Development and Toddler Years

The core principle#

Milestones get used two ways, and only one is valid.

Screening asks: is this child far enough outside the range that we should look more closely? That works.

Ranking asks: is my child ahead or behind? Within the normal range, that carries essentially no predictive information about intelligence, ability, or future achievement.

The ranges below are wide enough that most comparison between individual children is meaningless.

Development signals#

The signal that changes category: losing a skill already acquired is far more concerning than being late to gain one. Don't wait for the next scheduled visit.

Use routine well-child screening, and accept early-intervention evaluation when suggested. Evaluation is not a diagnosis and doesn't commit you to anything — and services help regardless of whether the child later proves to have been within the normal range all along.

On constant illness: preschoolers average 6–8 colds a year, each lasting about two weeks, concentrated in winter. If your child seems permanently sick from October to March, that is what normal looks like. Ear infections affect about a quarter by age one.

Supporting motor and language#

• Offer safe opportunities for floor movement and exploration
• Follow their attention and name what they're looking at — this works better than directing attention to what interests you
• Use conversational turns, gestures, songs, and interactive reading. Pause for a response and treat a gesture or sound as a turn
• Repeat and expand: child says "dog," you say "Yes, the brown dog is running." Confirms they were understood and adds structure without correcting
• Count communication across all home languages. A single-language word count systematically understates a bilingual child
• Don't quiz. "What's this? What's this?" turns interaction into assessment and makes it thinner
• Don't treat early walking or talking as a forecast of anything

Screen time#

Ask four questions: child, content, context, displacement.

• Babies and very young toddlers don't learn words from video — a well-replicated experimental finding called the video deficit. Marketing it as educational doesn't change it
• Preschoolers (roughly 3–5) genuinely can learn from well-designed, age-appropriate programming, especially with an adult discussing it
• Protect sleep, movement, conversation, relationships, and unstructured play first, then fit screens around them
• Heavy use is concerning because of what it replaces, not because of a proven hour threshold. There isn't one
• Video calls with family are interactive and different from passive viewing
• A show so an overwhelmed caregiver can reset is often a reasonable trade — the alternative isn't always better
• Current apps and algorithmic feeds are far less studied than television, so the older research transfers poorly in both directions
• Turn off autoplay; don't leave background TV running

Potty training#

• Earlier start = fewer diaper months but a longer process. That's the real trade-off, and it's a preference
• No benefit to intensive training before about 27 months — you extend the process without moving the finish line
• No method has been shown best. Skip guaranteed-three-day claims
• Align caregiver prompts, rewards, accident responses, and language. Including day care
• Treat constipation and painful stool early. This is the most common way training goes wrong: a painful stool → withholding → harder stool → real fear. Stickers don't address fear
• Stool toileting refusal affects about a quarter of children. Common, not a sign of anything unusual
• Nighttime dryness is a separate biological skill. Never shame or punish bedwetting

Discipline#

The active ingredient is predictability, not strictness or gentleness.

• Define one observable behavior and teach a replacement. "Being good" can't be reinforced because nobody knows when it happened
• Reinforce cooperation with specific positive attention — most parents comment far more on failure than success
• Use brief, predictable, feasible consequences
• A threatened-but-undelivered consequence teaches that persistence beats the rule. This is the most damaging common habit
• Don't lecture during a full tantrum. Keep everyone safe, wait for calm, then teach
• Align caregivers and follow through consistently — two systems produce no system
• Avoid spanking. No demonstrated benefit to behavior, and the better-controlled evidence links physical punishment to more behavior problems later
• Structured programs (1-2-3 Magic, The Incredible Years) work in trials. Pick the one you'll actually follow — a simpler system used consistently beats a better one used sporadically

Reading and preschool#

• Read together regularly, and interactively — ask open questions, let them choose and repeat, expand rather than quiz
• Skip products claiming to teach babies to read. Directly tested in controlled studies; they don't work
• Let a preschooler's interest guide letters and sounds. Formal reading starts at very different ages across countries, all with strong outcomes
• Choose preschool by teacher warmth, actual classroom interaction, safety, structure, logistics, and child fit — not by philosophy branding
• Evidence does not establish Montessori, Reggio Emilia, Waldorf, or any other approach as universally best. Two schools sharing a philosophy can be nothing alike
• Visit while children are present, and watch the teachers rather than the tour guide

Related:Questions for Clinicians, Parents, Childcare, and Family Decisions