How to stop being a playmate and still give attention

Your recent reply to a similar question really hit home and made a lot of sense to me. Often I feel like the kids want me to be their child playmate and imitate them and follow their instruction. I actively try to participate by giving them my attention, yet remain an observer and it is a balance that we struggle with at times. Recently, as I pull away from the play and observe, my daughter becomes concerned. She has asked me several times if I don't like what we are playing and if I don't like her and it breaks my heart. I always reassure that I love who she is and am happy to play whichever game she likes because I enjoy watching her create but she seems unsatisfied with this. Do you have any ideas on how to approach this situation from another angle? I find that after these sorts of interactions I go back to being the playmate to stop the tears and hurting. I'm sure there are other methods to apply and I just need some outside perspective, I would love to hear your thoughts.