advice for NK obsessed with "the heart"

Hi! sorry in advance this is so long, but I'm a first-time nanny (so of course this would happen to me) and got a great job with 5mo(M) and 7(F). From the first week of being there, the 7(F) started to obsessively talk ask "what is a stethoscope? what does a stethoscope do? do you ever feel weird when you go to the doctor and they have you take your shirt off?" I'm not thinking anything at this point because yeah, I remember going to the doctor as a kid WAS weird!Also, this all began with her favorite line, "my friend 7(F) has a question." She always brings this friend into the conversation which, at first, made me think she just was too embarrassed to ask "herself" but later made me think if all of this was from the friends experimenting while playing. However, this family has been in STRICT lockdown, and continue to be in one, since march (only leaving for the birth of 5mo(M) and that's it).From here, things only escalated. Every single day we would talk about stethoscopes, look up videos of stethoscopes, etc. Then, I made the mistake of telling her my watch tracks my heart rate so she says "can we find an app so we can check with your phone?" I'm like sure, I guess, and download some fake heart monitor app and now we're running around in the backyard for HOURS checking our heart rates. Her dad comes out and I mention that we're testing the hypothesis if running uphill or downhill makes our heart rates faster. he's a type-A parent so I'm like oh he'll love this, and he DID, but 7(F) starts freaking out and later tells me that we have to keep it a "secret". I used this time to touch on consent, but the day was over.After speaking about the situation with a friend (s/o to CFS) we conclude that I need to confide in the parents. So I tell the mom because I just couldn't discuss this with the father (this was like my second week!!) and she's just like not giving any reaction? I said something to the tune of "I just wanted to make you aware... so if y'all notice anything as well...." basically just that she's of age that she needs a talk that I should not have to facilitate.All that leads me to now, it's obvious there was NO conversation at all about this and now we watch videos on doctor checkups, play doctor constantly, and do anything that will "get her heart to beat fast" and then she'll feel her heart for like 5 minutes OR try to make me feel her heart. Every single time I'll just like lay my hand on her should for .2 seconds and be like "oh yeah".Also, I've tried everything in my arsenal to distract from acting uninterested, to bringing the baby into the game (she does not like this so I use it a lot lol) but she is obsessed!!What do I do? I'm glad I gave the mom a head's up so at least she knows this has been building if this comes to a weird point, and I don't want to have another talk with them, but I am honestly concerned and uncomfortable with the situation (also just over it!) via /r/Nanny https://ift.tt/3k1GkK4