How can I know for sure whether the girl is interested in me?

Well, I'll start from the beginning :D We met, when our parents decided to meet at her house because our parents are friends, so i can basically say that our families are old friends/ Anyway, she changed a lot since the last time i saw her and i immediately felt very interested in her, but i couldn't even ask her a question because I was too shy. Anyway, adults decided to take a walk outside on the terrace (i'm not sure) and spent all of them looking after her brother and sister. I'm pretty sure that she was happy when i started playing with the children as well and i believe that she was quite impressed. Anyway, after one day i found her profile on social network and we started chatting and still do. I think she liked my sense of humour and that i was attentive to everything she said. On wednesday we went to the cinema with her little bother and at that point I wasn't sure whether she liked me because she also brought her little brother. Basically we chat online every evening before she goes to bed. Oh yes!!! A bit back - when we left the cinema i could barely talk, i couldn't even open my mouth, well rarely. Tonight she decided to go to sleep earlier, although we usually chat during that time. Now I have no idea how to improve this relationship and move it forward. I also have no idea what she thinks of me right now. All the possible tips would be welcome :D please help)))