If I had to choose one piece of advice for young writers...

...it would be to step back and gain perspective, and realize that you will have six, maybe seven decades to write, but only one fleeting decade when your kids are little.  Realize that every "book review" they give you ("Read it again!") teaches you what works in picture books, and every silly conversation is a look into a child's mind.  Don't beat yourself up for not getting as much writing done as you'd like--you are doing the most valuable research that can ever be conducted in your picture book writing career!  Absorb, observe, but most importantly, treasure these days.  They won't come back.