>>Unbelievable. A baby must go through the steps of growing up by the book. Tolerances are less then a week.
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>>We have friends of this kind. Don't get me started.
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>>But then, over the years and a number of kids, it was odd to see the paediatric doctor changing. Thing 1 was below average weight. Was ok, to many fat ones anyway. 5a later, thing 3 was below too, but not as far. We had discussions about under - nourishing.
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>Our twin grandchildren, identical, at age of three, differ by a whole kilogram. And the lighter one is now actually taller. Both perfectly normal.

At the age of three we never checked weight. We know how under - nourish looks like, that was enough. If, at this age, they stop growing out of clothes, something is wrong.