New House Came With Ghosts

My parents just purchased their dream house 4 months ago. We barely moved them in before they started hearing unexplainable noises in the house. My sister and I each have 2 young daughters but, at times when none of the children were in the house, children's laughter and crying has been heard.
We have heard the sounds of a ball being bounced down the stairs and pulled out of the shower by calls of "Mommy" only to discover that our children are sound asleep.

My own personal experiences in the house have mostly been sounds, but , I have seen 2 apparitions.
The first one I heard was while I was in the restroom brushing my teeth. I heard a woman crying hysterically and then she cried out "Oh my God" and then went away. I ran out of the bathroom to check on my sister because I truly thought she was crying, but it was not her.
The first apparition I saw was also of a woman. I am a smoker but smoking is not allowed in my mother's home. I was out on the back patio having a smoke around 1 a.m. when I glanced in the kitchen window and saw a woman in a white (why do they always wear a white dress?). I ran inside to see who it was and I ran into my mom. She was wearing a nightgown but, hers was purple.
The second apparition I saw was a little girl. I saw her run into another room when I came to the basement to do laundry. I chased her because I thought it was my daughter, and, when I got into the next room no one was there.
Both of my sisters and my 12 year old daughter have witnessed this same apparition. We have seen and heard so many more things. Footsteps, falling dishes, laughing, talking, crying, etc. But, we have never been afraid of either visitor.
The little girl just wants to play like any 4 or 5 year old would. The woman does make me feel very sad when I sense her around.
We have not done any research on the house's history and do not know if the two are connected. We do plan to do some research soon. Maybe we'll learn something cool. Anyway's, that's my story. Hope you liked it.