We have constant meltdowns over nothing, little things and endless sooking from DS who turned 3 this week. I really think that it is a normal developmental stage - DS has great verbal communication for his age, but even so I think he gets super frustrated anyway. I think they have NO concept of why they can't have something they want, and this is developmental - can't remember where I read it recently. Our aim has simply to be consistent. It is tough to do but the thing we have seen work the best. I also turn to a blog called theparentingpassageway - maybe have a look there, she has some great articles on there that are based on developmental stage and behaviour etc. She is a Waldorf homeschooling mama so some things are a bit different but her approach resonates with me and if anything it is lovely to turn somewhere and know you aren't alone and it is all normal.
This too shall pass - surely!