When my children were young my fil and mil (in particular)" openly favoured our son , fussed over him, took an interest in everything he did, bought extravagant presents for him ...my daughter, two years younger, was effectively ignored, minimal interest shown, not listening when she wanted to tell them her news, presents costing pence instead of pounds and pounds for my son! Plus ignoring certain expectations that we had for our children, and encouraging our son to ignore us or answer back when we addressed certain behaviours! It took two visits like that ( they stayed with us) for me to say that we needed to talk ...it was really hard but we pointed out what was happening, why we were concerned, what our expectations were and what we would have to say to our children about their grandparents if it didn't stop. As ever there was a fairly "passive aggressive" response from my mil but we stuck to our guns and things improved. Over the years, a gentle reminder kept things generally on track! I do wonder if some would have gone for CO in these circumstances rather than addressing the issues openly and assertively (it was hard, as I said). If nothing else it made me very aware of what not to do as a grandparent ...not that that has necessarily stopped my fears of CO ...different issues!!