I might give up some of my adult collection to get back some of my childhood ponies (fortunately I still have all of my childhood ponies, so this is just a theoretical discussion
). But I wouldn't give up all my adult collection ponies to get back a few childhood ponies. Most of my adult collection I've had for 10-14 years, and I'm pretty sentimental about a lot of those ponies too.
As for picking between the two collections, it's really hard to say. I don't think I could give up my childhood ponies - but I have about 5 times as many ponies I've collected as an adult, and I'm really attached to most of them too. I can't imagine giving any of my ponies away!