We will conclude this introduction to phrases by looking briefly at phrases within phrases. Consider the NP:

[NP small children]

It consists of a Head children and a pre-Head string small. Now small is an adjective, so it is the Head of its own adjective phrase. We know this because it could be expanded to form a longer string:

very small children

Here, the adjective Head small has its own pre-Head string very:

[AP very small]

So in small children, we have an AP small embedded with the NP small children. We represent this as follows:

[NP [AP small] children]

All but the simplest phrases will contain smaller phrases within them. Here's another example:

[PP across the road]

Here, the Head is across, and the post-Head string is the road. Now we know that the road is itself an NP -- its Head is road, and it has a pre-Head string the. So we have an NP within the PP:

[PP across [NP the road]]

When you examine phrases, remember to look out for other phrases within them.