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Baby Pajama Sizes: How to Pick the Right One

Updated 2026-11-12

Toddler pajama set with a dinosaur print

Baby sizes are labelled by age, but the age is only a rough guide. Brands size by height and weight, and those charts differ from one label to the next.

How the labels work

  • Newborn, 0-3M, 3-6M, 6-9M, 12M, 18M, 24M are baby sizes, usually for one-piece sleepers.
  • 2T to 5T are toddler sizes, cut for kids who walk, with more room in the seat and less in the body.
  • 18M and 2T are close in length but cut differently: 2T assumes no bulky diaper and a slimmer build.

Picking the size

  1. Weigh and measure your child. Height matters most for footed sleepers, because the feet stop them from stretching.
  2. Check the brand's own chart. Every listing has one. Use it rather than the age on the label.
  3. Between sizes? Go up one. Except on snug-fit sets, where the close fit is part of the safety design.
  4. Think about the season. Buy the next size for winter pajamas if your child will grow into it by the cold months.

Picks to look at

Koala print cotton bodysuits, 5-pack
Koala print cotton bodysuits, 5-packFive short-sleeve cotton bodysuits in soft greys and greens, with koala prints and slogans.
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Plush koala hooded bathrobe
Plush koala hooded bathrobeA soft grey plush bathrobe with a koala-face hood, ears and a tie belt for after bath time.
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Hooded puffer snowsuit with bear ears
Hooded puffer snowsuit with bear earsA black quilted one-piece snowsuit with a fleece-lined hood, bear ears and a full zip.
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Striped zip sleeper with fox patch
Striped zip sleeper with fox patchA teal striped cotton sleeper with a zip front, ribbed cuffs and a fox applique.
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Picks to look at

Zip-front footies with jungle animals, 4-pack
Zip-front footies with jungle animals, 4-packFour cotton footed sleepers with stripes, elephants and giraffes, and a zip front for quick night changes.
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Pink and grey footies, 4-pack
Pink and grey footies, 4-packFour footed sleepers with rainbows, dots, flowers and a bear face with soft ears, all with zip fronts.
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Fleece footed pajamas, 3-pack
Fleece footed pajamas, 3-packWarm, flame-resistant fleece one-pieces with forest animals, a moose patch and a red buffalo check.
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Cotton star-print sleepers, 3-pack
Cotton star-print sleepers, 3-packSoft cotton footed sleepers with stars and planets and a zip that runs down the side of the leg.
Check price on Amazon