How to handle the delicate situation of your child seeing you making out?

In our case both of children sleep with us in the same room. We are trying to get the elder one who is 9 years to take a room of her own but she insists she wants to stay on with us.
The younger one is just 9 months old so she needs us to be next to her anyway.
Just in case the elder one sees us in the act (as we can't use a different room it being a joint family) how do we react especially she doesn't know we have noticed and she says nothing about it.
Hopefully hasn't happened so far but could happen if she wakes up in the middle of the night and we don't notice.
How to handle the delicate situation of your child seeing you making out?
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