|Brynne with cousin that's five months younger.|
|Hadley with her cousin that's 10 months younger.|
As an example, let's look at the nursery at church.
Our girls go to the toddler class, which is, roughly, 18 to 36 months of age. If that class is a little crowded, and the 36 to 50 month class is not, a child can be moved from the younger class to the older one (after parental consent is obtained). Our girls, at 23 months, are way less developed than the three to five year old children in the class ahead of them. By lining them up, and moving the tallest, you would do our girls a huge disservice.
Four year old + cup of water = hydrated child
23 month old + cup of water = wet child, wet clothes, wet table, wet carpet
That's just one example. Here's another:
The four year olds can, for the most part, communicate with others. Sure, they have language patterns that can be tough to discern, but you can get the gist of what they're saying, as can other four year olds. The 23 month olds are limited to what they can express, and so frustration (screaming, tantrums, and tears) can ensue. Not only between child and adult, but between children.
Not convinced? Here's my final example.
Four year olds should be stronger than 23 month olds, and can, therefore, take what they want by force. Even if they're not trying to be mean, they still are dominant. They might both be going for the same toy. If the four year old accidentally bumps the younger child, he (or she) is going down. Now, we're talking real tears and screaming.
This may serve more as a reminder for myself than as education to anyone else, but it may help someone. If at all possible, ask the parent for the child's age before making that assumption. This is especially helpful if you're looking for an age appropriate toy to give to a child.