Oh dear I feel for you and your DD. However this must stop, at 18 months he knows he has control! It's time to turn the tables and be very hard . Your daughter must not worry too much about his finer feelings - they don't have many at this age! They are definitely self interested - that is normal. Put him in his cot say night night , and leave the room . I know it is hard and I understand that she is desperate for sleep for herself and her son , hence allowing the boob fondling - I get why she does that ! However........... by permitting that she is rewarding him for making those demands!! Ask her to harden her heart ,do not return to his room and NO. more leaning over his cot to comfort him. It will be very stressful indeed but no pain no gain , I do hope she / they can persevere. Another idea if that does fail ( doubt it will ) if her OH is male send him upstairs to their son - no chance of boob comfort then! Ask your DD to be consistent and firm , her son will eventually get the message and will not hold her actions against her ! She will be doing him a favour in the long run! As you say she has had a tough time conceiving and giving birth ,this is probably the root of her feelings. I wish her luck , while she is persevering with this new routine I know you will reassure her she is a good mum - because she is !! I wish her luck , hope she sticks to her guns and that the new regime pays off . Hard to do I know that but she must have courage and determination if she is to be successful, it will be well worth it eventually. If she really finds ignoring his crying too much to bear ask her to send someone else upstate - whatever happens - no more boob fondling!!!!!! Good luck .