DH has a 9 year old daughter and we met when she was 1 and her parents had been separated since she was 3 months old. We have three further children and until April had my DSD every other weekend and extra in holidays. I often looked after her alone and we were really close. In April DH refused to swap weekends so his DD could attend an event with her mum and DSDs mum was really angry and said DSD felt betrayed and would only come for contact for the day for the foreseeable future and not stay over, even in holidays.
DSD lives about 40 miles away and her mum wasn't willing to do any travelling to accommodate this new arrangement so - without discussing it with me - he told his DD/her mum that it wasn't worth it and that he'd only collect her if she'd stay over. He hasn't heard from them since.
There's already a court order but DSDs mum doesn't think much of breaking it and DH thinks that therefore means it's pointless returning to court. He talks about DSD in passing, and seems to be of the opinion that she'll think he was reasonable when 'she gets back in touch when she's older' 
I miss her desperately and worry so much about how abandoned she must feel. I was pregnant last time I saw her and she was so excited about the baby but now must feel replaced by her. My DC miss her lots too and I really don't want them to just lose her from their lives. I've spoken to DH but he won't budge on backing down. I don't know how it would be received but I feel like contacting DSDs mum and asking if the DC can at least have some contact. AIBU?