You got the "Four is enough" message because you now have reached (and surpassed) the number of four kids. You had two kids, then jumped straight to five, without arriving at three or four kids.

But they didn't count the adopted girl. It just counted the little boy and the triplets.
In my family with six kids I got the Five and the Six message when I reached those numbers. None of them are adopted though.
It's like they aren't counting the adopted girl. She is .... strange though. When she plays with the toys her head spins around and around. It's really creepy.

The triplets names are Sandria, Cariana, and Paprika.

Ok, lemme see if I can explain this in a way that makes sense...

Before the triplets you had 2 children including the adopted girl, right? So, when the triplets were born you had 5?

The "birth" or dropping of the triplets put you past the "Four is enough" trophy. You didn't receive a '5 kids' trophy because there isn't one. If your family has one more child, you will receive the '6 kids' trophy because your family will have 6 children.

They are not excluding the adopted child.

That's not what I'm saying. I'm saying I got a message (Not the four is enough message but another message) that says this family has four kids total. They don't. They have five. The message didn't count the adopted girl.

What sort of message? I can't ever remember seeing a message like that, apart from the trophy message. Go to the parents' Details screens. How many kids are shown?

In your original post you said:

When the triplets were born I got a message that Four is enough. It didn't count the adopted girl. It's like she doesn't exist.

As has been explained, because you went past 4 with triplets, and there is no message for 5 kids, you received it after the triplets were born.

There are only 2 messages - 4 is enough, and No Vacancy after 6 kids.

Sorry, it wasn't a message it was an email. It was an email message to me stating that they now have four kids.

There is no such email!

Yep, been playing a while now and I agree. There is no such email. What you got was the notice that you had fulfilled the trophy that is Four Is Enough. Even if your adopted child had actually been born to them, you still would have received that trophy message because as soon as you have four kids OR FIVE then you get that message to let you know that you accomplished getting that trophy.

It has nothing at all to do with the fact that the child was adopted.