you can do it without...I don't tend to buy patterns for childrens clothes but take a paper (usually newspaper) pattern from something that you know fits and you like. Remember to leave extra for darts/gathers/hems etc. If this is too hard than there are quite a few free downloadable patterns on the web for basics. Simple pinafores you might be able to just measure and cut if you are confident and careful. Happy sewing
I am with joruth on this, I hardly ever use a pattern, often taking apart things that I like the shape of, but not neccessarily the material. I make newspaper patterns. I also modify off the cuff as well, often these are the most loose fit clothes that are great with a belt. You may make a few mistakes on the way, wonky hems or tight armholes, but they are part of the learning process.
I am one of those that loves to make for others, especially my neice, but not for myself.