is it ok to choose who you or your kids hang out with? (looong post)

I feel so bad right now, I hate doing things and then feeling bad about those things.

Last week dh and I were having a normal evening, he was mowing the lawn in the front of our house, the kids were playing, and I was finishing up cooking dinner. The table was set, everything was ready to go and I heard someone outside screeming "does Carmen live here?" I looked and it was someone in a car talking to my husband asking him if Carmen lived here. He said yes as I came out and inside the car was a very, very distant cousin that I have seen about twice in my life (I lived in Chile since I was born until 3 years ago so there's people in my town that are probably related to me in some way but I have no clue) so she's jumping and saying how excited she is that we live about 2 blocks away from each other and she asks if we would like some company. Well, my obvious polite answer was "sure" but what was I supposed to say? to hell with our peaceful family dinner, I guess. So she, her mom and her unbuckled 4 year old in the back seat (no car seat OR seat belt) parked her car and came in. They wanted a "tour" of our house so we showed them around. We sat down in the living room and talked for a while and then my cousin asks if we have dessert so I say no, we don't just yet. So she offers to go get some ice cream for everyone and come right back. She even told us we could have dinner while she was getting the icecream (gee, thanks!) and I told her she could leave her daughter since she and my daughter were already playing barbies in my daughter's room.
I told my husband we might as well eat dinner since it was already 8 pm (it was about 7 pm, our dinnertime, when they first came) and who knows when they would leave. So we sat down and asked the little girl if she wanted to join us, she said sure. So I served dinner and when she was done she said in a rather, slang way of speaking, that she didn't want anymore. That was fine with me, I let my daughter excuse herself early from the table to go play with the little girl, while dh and I finished dinner with our son (16 months old) and kept looking at each other in shock over this whole situation.
Then, the other 2 people return with the icecream for everyone, and she tells me "I called my other daughter and her friend and "they're both comin' up". So I figured that meant that she had invited more members of her family. So as we are eating the icecream, two girls STORM in through our front door, literally SLAM the door open, come running to where we were, and they start talking with the 2 people that invited them (my cousin and her mom) without even LOOKING at my husband or myself. Note that I had never seen these two people in my life. ever.

So.. about 2 hours later, around 10:30, they leave. Before that she asked for my number and told me we could do playdates with the girls all the time since we live so close by, and etc..

When they leave, I am in SHOCK and call my mom immediately and she said that there is a distant part of our family that is like this although she does understand this being shocking to me because we grew up very differently.

Today I got a call from them asking us if we wanted to come over to play in their pool. I said we couldn't, but thanks so much for the invitation. I felt terribly guilty and like a "mean girl" because I heard the little girl in the backround say "why can't Valentina come play with us" (Valentina is my daughter) that really made me feel awful because I had to make a decision, and that decision is that I don't want to hang out with them. I also (and my husband too, I must add, although me, perhaps, a bit more) don't want Valentina learning these bad habits (not using a carseat, swearing -oh, they swear a lot and in my house we hardly say "shoot"- and slang language.

So anyway, I feel guilty because of the little girl, mostly. My cousin told me that someone watches her about 10 hours a day for $2 an hour, and when she told me that my gut instinct was to offer to watch her for free because I imagined that the type of care she received must not be very good. My husband told me not to do this, and that I couldn't save the world and that I hardly had any time left with my kids, LLL and just being a SAHM. (oh, I also work part time some evenings, lol)

so anyway, am I completely wrong?? I feel guilty but I feel I made the right decision, though. What should I say or do if they show up unannounced again? what if they continue to call with invitations to come over?

Thanks, ladies