Not sure how I should take this.

I was sitting at the table eating with my daughters at Thankful Thursday. My 10-year-old comes over to the table where my nine-year-old was sitting and whisper to her, "come here let me talk to you". My 10-year-old then reply, "what now"? I'll looked at them both and asked "what's going on"? They both stated, "nothing mama" and walked away.
I am so glad that my daughters have that same close relationship that my sisters and I share. But where do they get off thinking they can have secrets and when I asked them what's going on they can't tell me. I'm going to get to the bottom of this because they are not grown.