I too have tried to limit what toys grandparents, aunts, uncles etc bought for my kids and while it was ok for a while, I have to be careful b/c most of those people didn't have the money to buy all the wooden toys or all the natural non battery toys that I wanted my kids to have. I finally had to let it go. It was more important that my inlaws and my family were happy and my kids were happy. I would rather my children have a wonderful relationship with their grandparents and aunts and uncles no matter what toys they get.
Now, for the ATV issue. Sounds like by the price its one of the battery operated type of ATV which are safer than the real atv but still need to be cautious. My sil bought one of these at a garage sale for my older ds. While I was not thrilled at the idea, my ds absolutely LOVES to ride that thing around my inlaws farm til the battery runs dead LOL!!! He was just over 4 yrs old when he got that. So, 3 yrs is a bit young but not a bad gift especially if she loves it. I got over the idea of him having it. It makes my child happy then I am happy.
Now, we are very cautious when he rides it. He can not ride it w/o an adult outside with him. He can go down the extra driveway to the pasture but has to turn around at the gate. If Grandpa is coming in the driveway with a tractor (inlaws are farmers) ds has to drive the atv to where we are and stop and get off. He is not allowed in the driveway when Grandpa has a tractor running. He knows not to run the atv around his little brothers either. We have not had a problem with it at all.
I guess sometimes, we need to let go of what we want for the happiness of our kids.