Hi Katy
I remember DS#1 did something similiar at around the same age (15mo). I was heavily pregnant then, so DH did all the work:D
I remember him saying, that after a few time of going in and out DH just told him to "go to sleep" in a firm voice. He was as shock as I was that DS#1 listened. I dont think it would have worked if it was me
When DS#1 was around 15-20 mo there was a bit a NW. As they get older, they can comprehend a bit more, (I am having SA prob with #2 atm
)I remember telling him to close his eyes, I stayed, but no contact and when he opened them and saw that I was still there, he closed them again and eventually fell asleep.
I gave him a lots of reassurrance, coz for us we were expecting/had #2 around that time and I didn't want him to feel neglected (17.5 month gap). It it went away by itself.
HTH