One of the biggest problems is that there are so many different concepts and equations in algebra and in order to be successful you have to understand the entirety of it or you will not be able to figure out which procedure to use. You learned the order of operations years ago and that is one key tool for algebra. This tool allows you to understand which process happens first and so on. PEMDAS is a very valuable tool.
Children may also get started with money, time, and measuring, though it is not absolutely necessary to master any of that. The teacher should keep it playful, supply measuring cups, scales, clocks, and coins to have around, and answer questions.