The expression としては is used to set a frame of reference or standard for evaluation. It means "for a ~", "as a ~", or "considering that ~ is", and is used when you want to judge or comment on something relative to a particular role, category, or identity.
It is formed by attaching としては to a noun. The particle として means "as" or "in the capacity of", and adding は highlights that noun as the standard against which the following statement is measured.
The most common use of としては is to evaluate something by the standards of a particular group or category. The implication is often that the result is surprising or noteworthy given that standard.
Here, the speaker is saying the quality exceeds what you'd normally expect at that price, or that the essay is impressive relative to the standard of children.
としては can also express someone's standpoint, role, or position – what they think or how they feel in their capacity as something.
In these cases, the speaker is framing their opinion or decision within the context of a particular role.
While として simply means "as" or "in the role of," adding は introduces a contrastive or evaluative nuance. Compare:
としては often pairs with expressions like まだまだ (still not enough), なかなか (quite/fairly), めずらしい珍しい (rare/unusual), or comparative/superlative expressions to highlight that something deviates from the norm for that category.