New and overwhelmed!

I had an instance yesterday that was frustrating and happens quite a lot. Both girls are 50% of the time very aloof and seem to care less whether we are with them or not. Then the next time they see us they are very affectionate and totally engaged in everything. Is this normal?They are always saying they want to be adopted by us or no one. So I really think they want this as much as we do. Should I follow their lead, and if they aren't engaged not push them. I asked the 8 year old yesterday if she ever missed me and she just said sometimes and ran out the door to her ride. I'm always so excited to see them, but often they are indifferent. Any insight?