Not everything that looks like a preposition actually behaves like one. For example, the word to followed by a verb phrase forms an infinitive phrase. These infinitive phrases, which we will examine more closely in a later chapter, are verb phrases, not prepositional phrases. We can see this if we contrast infinitive to with the preposition.
(1a) My kids always want [to go] [to Disneyland].
In this sentence, the verb want has two constituents that begin with to, but the first is followed by the verb go, and the second by an NP. There are several ways in which the first instance of to behaves very differently from the second.
Most prepositions, including to, allow the degree words right or straight. The infinitive marker does not:
(1b) My kids always want to go straight to Disneyland.
(1c) *My kids always want straight to go to Disneyland.
The infinitive marker also permits ellipsis. That is, the verb phrase after the infinitive marker can be omitted if it can be understood from context. The preposition cannot:
(1d) My kids always want to.
(1e) *My kids always want to go to.
Finally, if we say that infinitive to is a preposition, we must conclude that "to go to Disneyland" functions as a PP, but notice that other PPs cannot be substituted for an infinitive phrase:
(1f) *My kids always want to Disneyland.
(1g) *My kids always want by the car.
We will label the infinitive marker INF, but will not analyze the structure of infinitive phrases until later.