Hi, L.. I, also, had no childhood, no real mothering or fathering, and had to figure out what to do the best I could. I suggest watching other mothers and kids at play in order to learn what they do, and then do what you and your kids like.
I would start with using a toy that you know they like and that you sort of like, too. Let them lead you a bit, since you're rusty at playing, but don't let them rule you. Building stuff like using Leggos is usually pretty safe; everyone on the floor can build his or her own little tower or house, and you can all put them together and make a neighborhood or a town. This can lead into more social play where you play-act neighbors and friends or something.
Try singing with them. Teach them a kids' song. If you don't know any, get a CD with children's music and all three of you can learn it together. Kids LOVE singing. Ask Daddy to help you learn how to play, too.
I think that some of the yelling, aside from being the only parenting that was thrown at you, comes out of the insecurities that you were left with (not your fault) and also the anger you still have at your parents for not letting you have a childhood (also not your fault, but you have to let go of it). Do you have some secret jealousy that your kids get to be kids, but you didn't? Don't be ashamed, I felt that, too. My whole childhood was destroyed in the worst ways, over and over again. For my healing, and for your healing, that has to be let go of, forgiving the parents who didn't know any better (or were drunk or stoned), and focus on how beautiful and sweet and smart these children are.
Focus on what gifts you have been given. Focus on what's wonderful about these kids who don't have to suffer what you suffered. This all takes practice...but the first steps are letting go of what still hurts.
Forgiveness is not for the benefit of the people who have hurt you and me, but for yourself. These people who hurt us do not feel our resentment or our pain...they have no idea. Letting go can only free you to live in the present and create a wonderful future.
If you believe in God, place these hurts in His hands as you forgive. Leave the justice of the matter up to Him. He's really, really good at it, even if we don't get to see how He evens the score (and loads us down with uncountable blessings besides).
I will say a prayer for your growth as a mom. I hope that you will find tremendous joy and let go of all the anguish.
Peace & hugs,
Syl