Meeting his children

My bf and I are having a baby girl. He wants me to meet his kids from his previous relationship. Boy, 8. Girl, 10. I’m having so many mixed emotions with finally meeting them. This is a new experience for me. I knew the day would come but now that it’s here, I’m wondering What do I say? What do I do? I really don’t know what to expect. I asked how he wants to introduce me and he hadn’t really thought much about it. I don’t really want things to be awkward or a disaster. Any suggestions ?