I've been feeding my daughter store-bought baby food in glass jars, but I plan on starting to make her food myself. Is it safe to wash and re-use the jars I already have?
So, for as long as you aren't planning to freeze (cold temperature) or start canning food (hot temperature) for long-term storage, you should be fine.
We used the baby food jars in the beginning, and now we use them for various things like carrying drinks (water/milk/juice) for our little one, or carrying snacks/food in it when we are out and about. It works pretty well for us.