"I aim to have three children."
Translation:Ik streef ernaar om drie kinderen te hebben.
Grammatically is not incorrect, but it's an odd way to phrase it, just like it is in English. The original sentence is odd as well, granted. I doubt anyone would phrase it like that.
That being said, the problem here is the wording, since your sentence comes to 'my goal is to have three children'.
Semantically, it's the same, but as the wording is different....