I can totally understand how you feel OP- it is a big wrench to lose a part of your childhood in this way. BUT, and it' is a big but, please don't weigh your parents down with how sad you feel about it. I say this from difficult recent experience with in laws.
In laws decided to sell their house having lived their for 44 years. They just weren't enjoying their retirement as the garden was huge and needed lots of work, constant house upkeep, had to drive to even buy milk etc. it was a huge wrench for mother in law, but she fell in love with a great house in the centre of a nearby village. She and FIL were very practical about the whole thing and threw themselves into gutting and updating old house to get best possible sales price . They were sad on moving day, but the new house has transformed them. They spent a year doing everything they wanted to In it, have made loads of new friends in the village, walk to the pub and shops, save money by hardly using the car etc.
DH was sad but equally practical and positive for his parents, taking a week off to help them declutter, sell antiques, ebaying and boot fair etc. SIL however ( aged 46 at the time, married in own house nearby) threw a massive strop, tried to push us into buying half the house so it was kept in the family ( and she could live in it!), dithered about sorting out the mass of her stuff which was still in the house, criticised the new house, kept going on about how terrible it was for her etc. DH in the end had to " have a word".
Can you try and have a last lovely weekend there, take lots of photos of family, dig all the old albums out etc and have a nostalgia day? DH organised this for his parents and this year we gave them a big album with all those photos in, plus some from the housewarming party we persuaded them to have in the new place. They loved it and are so happy they now say they can't imagine why they didn't move sooner!
I know it is hard, but please try to be happy for them in a new chapter of their lives.