Should My Boyfriend Go Out With His Ex Wife And Kids? This Really Upsets Me.

It's not up to anyone to decide for you not to get hurt my dear. Are you hurt? You said it's upsetting you, this means you don't agree. Yea it's true you'll have to learn to accept that he has a past life with kids but doesn't necessary means he has to spend time with his ex-wife (O_o). Spending time with his kids are what he's suppose to do but with his ex as well... Umm I don't think so. The only thing he needs to talk with her should only be about the kids, it doesn't mean they can't be friends though. He'll have to understand your feelings too that you don't like him spending time with his ex and he shouldn't use his kids as an excuse.
Let him know that how you feel and let him know he shouldn't use his kids for an excuse to spend time with her. If he's going to go out with her, have him take you along too. That way you can get to know each other. Forget what his ex is trying to do or say, it's about you and him. Remember, no one can tell you how to be hurt or disagree. Take care.

NO NO NO!!  If he is committed to you than he should not be spending time with his ex wife outside of reasons to do with the kids.  It's very disrespectful in my opinion and if his intentions with you are genuine, then he should NOT be a "family" with his ex and kids.

I understand him seeing his kids and doing those thing with the kids, but I would draw the line with him hanging out with her.

Nuh uh, no way!  This is complete b.s.  These kids are old enough for your guy to take them out and do stuff with them.  Going to the bm's house is not ok.  
He sounds like a selfish jerk!

If your boyfriend is aware of your feelings and love you he will make some changes to satisfy you as well as continue the relationship as parent.
The children are not babies, and he does not have to visit them in the Mother's home. If you both are wishing to have a life together, he should have time with you and the children together. Many people can even spend the night at the ex's home with the children and never consider a relationship of the sexual nature with that ex-mate. I don't think it is healthy because the children, regardless of age, may have it in the mind that they will be a family again.
If this bothers you and the boyfriend offer insufficient reasons, move on. There are always things that will be of concern when either mate or both mates already have children.

I know I feel the same way when my boyfriend visit his kids I feel upset too I don't know why even if he spent more time with me maybe bec I know that when he visits his baby he go to his ex wife and thats what bothers me amd he also keep picture of his kids and ex wife in our computer

I am in the same situation... Not good is it:

Absolutely not, she has her time and he has his it shouldn't be shared it will confuse the kids.

No you should not, especially when your not even invited. Why aren't they at his place? Spending time with you and him.