Kids should start getting an allowance at three years of age. There are two core reasons for this advice.
If you learned about money as a child, it wouldn’t stress you out as an adult.
Does speaking your native language stress you out? No, it’s natural to you. That’s because you were taught how to speak at a very young age. There was no pressure to “get it right.” Every word was celebrated and encouraged! Now imagine if you had the same luxury in learning about money. It’s not hard to be a master at something, even complicated subjects, if you have an ocean of time and you are continuously learning the information in bite-size pieces.
Most adults only have the financial education they learned through osmosis from family and friends. At the very best, this education is incomplete, but for most, it’s a downright handicap. The average American family has about $16K of credit card debt. WTF? (What happened to the land of the free?!) Even if you have no credit card debt, chances are high that money management feels stressful. It’s common to think that the ONLY way to eliminate financial stress is to simply earn more money. That’s not true. If you make more you, will spend more. (Economists call this the wealth effect.) The way to end financial stress is to learn how to fund multiple goals, on a seemingly limited budget, easily. If you haven’t been taught how to do that it will feel like an overwhelming, seemingly impossible, request.
You learn by doing.
If you buy presents for your child (not including birthday or holiday gifts; but the “just because you asked gifts”), they will learn how to ask, beg, plead, charm, and pout. One day they get what they want, one day they don’t. This can be very confusing for a child. They start that “getting things” just “magically” happens. Children learn by doing. (We all do!) This is the only way the information becomes “real.” When children are given money to spend, they naturally start to learn how to weigh the value, budget, and save. These three skills are priceless. Almost all adults know how to “earn” money, but the struggle comes with budgeting their money. When my clients start the Millionaire Boot camp™, the number one request in most cases is: “Help me create a budget that makes me feel like I’m still living!” If we all started practicing the art of budgeting at age three, by the time we were adults we would be masters, not beginners.
Be consistent
To get started, there are only two steps. Step one is being consistent. It’s imperative that you aren’t wishy washy. Wishy washy is defined as sometimes you buy a toy for your child because they ask, and sometimes you tell them to use their allowance. This is confusing, and will destroy exactly what you are trying to create. (there will be no need to budget, save, or weigh the value of two toys against each other, if your child thinks they can rope you into getting both for them.) Therefore, I do not buy my son any toys, except on this birthday and holidays. This is hard. Not for my son, but for me! I want to see his face break into a smile. I want him to reward me with hugs and kisses for getting him this new toy. However, if you really want to give your child the ultimate gift, a life free from financial stress, there can be no exceptions to this rule. Be consistent or don’t even bother.
Give them enough money
The second step is deciding how much the allowance should be. The tendency is to make is a couple of dollars. However, this is often too little. A better way is to estimate how much you spend on toys per month. If it’s $50, give them $50 as allowance. It might sound like a lot of money, but if the child is used to getting two toys a month, it’s imperative that you start with what they are used to receiving. You want them to learn to manage their money, not feel the restriction of not having enough money. There is plenty of time for that later. 
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