Moms: stop saying to other moms, whose children are younger than yours, or perhaps haven't hit the developmental milestones yours have, "just you wait...".
If the words start to cross your mind, as another mom is talking (or maybe even complaining) about how busy it is to have a crawler or how her child has just started saying "mama" or perhaps has recently started some bad behaviors, reconsider using them. Stop for a second, and think about how fantastically overwhelming it is to be someone's mother. Remember how you felt when your child was in that place. Hell, remember how you felt this morning when your kid was running around sans diaper, spilling milk all over the carpet and climbing on the kitchen table to play with your sewing needles when you tried to clean it up. Did you, at that moment, need someone to tell you "just wait, it'll get worse!"? Of course not. Who needs that, ever, really?
All we're ever looking for is for someone else who understands; who knows how stressful motherhood can be - at every phase - and can smile on the other side of it. Someone who says, "Oh yeah, I remember that. Those days were tough. But then he learned how to say 'I love you' and let me tell you - that is awesome!".
If you want to tell another mom to "just wait", tell her about the awesome things coming her way. Help her look forward to her child's development instead of mourning her baby growing up. And for the love of God, stop the fear mongering. Let her enjoy what she's going through, or vent if she needs to, and she'll do the same for you.
It never seems to be said enough that moms need to be spending more time supporting each other and less time judging. What we do is hard, awesome stuff. Being someone's mother is fantastic. Fantastically overwhelming, but especially fantastic.