Me and my child's mother wer together four 3years I won't her back she left me because she said I was crazy when she left she was6 mouths pregnant we don't talk any more its been 8 mouths since we have been broke up she lives with her mom with both the kids is there any way I can get her back or is 8 mouths 2 long

Unfortanetly you can't make her want you back, If she said you were crazy.. However you can improve yourself. Did you try to seek counseling??
I know you probably love her and she loves you but she is probably afraid to take you back, you have to take action and seek help, she needs to see that you are trying to help yourself. As far as you and her establishing a relationship, before you try to get her back and make things worse I think you should try to work on yourself, what have you done differently or what have you improved since the breakup? Because If the answer is nothing then I hate to tell you she is more than likely not going to take you back, and even if you do change, it really depends on how much emotional damage you have caused...

If your drinking or doing drugs, completely stop. Go to aa, anything positive. Tell her, and also ask her to go to couple counselling. Are you working, if not start working. Pray . Pay maintenance, and also take kids out. Not to see her, but just do it because u want to see them. Go to gym/ get a dog and walk it loads. Exercise.do this all for 6 months, and there is a good chance she may want you.
Do these things for yourself, not as a trick. You will be surprised at results. Good luck.

Save up, tell her your saving to take the kids on a holiday in say 6 months. Say you would like her to go. You will get separate rooms if she wants to be just friends. Be a good man.

Also be nice to her mother. She has been helping your kids, I am sure. Respect her. Invite her on vacation too if you do all go.

The man thing to do, regardless if you get her back or not, is to go to the court house, and set up child support. Then work on getting yourself together, and see about visitation with your kids. That's the man thing to do. You seem more concerned with her, than your own blood, so rearange your priorities, as a man.