How can I find out if my house is haunted, my 2 year old wakes most nights screaming, telling someone called Sam to go away, he then screams no, no, out, out, this occurs on several occasions throughout the week, the same each time, any one help us.

If she is waking up screaming rather than waking up and then screaming she most likely is having a reoccuring dream rather than a ghost.
When she wakes up screaming and after she calms down ask her to describe everything she can remember. If she tells you she is seeing something in the house or that something is waking her it might be a ghost.
If she says stuff like running down a path or something that doesn't have to do with the house then it is probably a reoccuring dream.

It sounds as though you may have some activity going on. Spirits are attracted to young children. Try setting up a video recorder in his room that has the capability to record at night. If it doesn't have a night vision option you want the lowest Lux possible. Also get a digital voice recorder and place it in the child's room while he sleeps. You may be surprised by what you hear and see during playback. Also do some research on the home or property that you reside in. You can do this by going to your local library or towns historic society if you have one. Find out if anything unusual has ever happened there such as a murder, a suicide or fire. It is possible that there was indeed a Sam that lived there in the past who suffered an unfortunate death.