DD is 6 months and we started her on solids earlier this week.
What you're encountering sounds pretty normal to me. Since you've only offered the cereal a couple times, she's still learning what to do with her tongue. I remember Kevin putting his hands in his mouth while feeding solids too. I think it's just an exploration thing, particularly if she's an avid hand sucker. As long as you keep the quantity of solids low and always offer breastmilk first (and sometimes after too), it's all good.
I hope that helps! Let us know if you have any additional questions.