Pattern re-sizing: adult patterns to children's size and infants to toddlers

[LeLyMa]

Ok, I'm sure lots of people have asked but I still haven't figured out how to grade patterns several sizes bigger or smaller. I have tons of adult patterns that I think would be ok for a toddler. None are fitted so no darts, etc and simple shapes, but I have no idea on how to make the pieces small enough for a kid. My daughter would wear about a 4/5 and the patterns are women's 6/8. I also have a few patterns that kids 7/8 that I nned to grade down for her and some infants 18-24mo sizes I need to grade up. Is there software I can plug in the different measurements and it will grade for me? Are there formulas I can use? Sorry I have no idea where to begin

I can post the pattern numbers if needed. I just have tons of patterns I'm going to try and do.