One caution. yes, I've frequently heard that the best edit is to rip out the first 50 pages. As I read people's first drafts, I can understand that. I had to yank out 2.5 chapters of my recent YA. At least I figured it out before I got through Chapter 7. I think that might be improvement.
The caution though? Don't destroy those pages. Save them. In my case, I did have a reason for those chapters, but I decided that I needed to cover those reasons at other points in the manuscript. I was able to salvage almost 60% of it, dispersing small chunks here and there and I'm not done.
So also consider why you had those chapters in the first place. Does it contain your main character description that was wonderful? Does it set up the beginning of the conflict? Does it describe your setting? Those are typical first chapter setups. You might find that your manuscript will be richer with the addition of a few paragraphs here or there. You might also realize that your set up for the conflict is lacking it's launching platform.
That doesn't mean you want the whole 50 pages or whatever. Go through them and highlight what you think is essential to the rest of the manuscript. It's rather fun really, you get to find the important bits, examine them as to just how good they are, and then find just the right place to land that paragraph or that flashback, whatever.
Good luck with killing the babies, but be careful--some might well belong.