Many of the stories I hear from returning adult bike riders involve a fear of riding derived from experiences as a child. The most common one (especially among women) is, “My parents bought me a bike that was too big, and said I’d grow into it. I fell off of it too many times before I grew into it, got scared of it, and didn’t ride a bike after that.” Now, as adults, they want to step back into the world of bike riding – their knees are bad; their friends ride and they want to join; they want to experience the magic of being on two wheels.
I completely understand the balance that parents have to strike with economic necessity and a growing child. If you buy a bike for a kid that fits perfectly now, will they have a growth spurt in a few months that then makes the bike too small? How can you tell what bike will fit for what length of time? If you buy a department store bike, that’s less expensive – but may be more costly in terms of maintenance, repairs, and safety issues. (For the record, I advocate for bike accessibility, which may include a cost factor; but when discussing a department store bike purchase, I always tell parents to bring the bike to a local bike shop for a tune up before their child rides it.)
In Tennessee, state law requires riders under 16 to wear a helmet. This cost needs to be factored into a bike purchase as well. The easiest way to figure out what size helmet your kid needs is to start by measuring their head! Most helmets will come with a size range that accommodates, say, 49-52cm. You should look for helmets that come with a rachet in the back that can be adjusted to fit a growing noggin. (See the CPSC helmet sizing guide for more detailed information.)
“My kid has a big head! Can they wear an adult helmet?” The answer here is mixed but for the most part, no – the way a kid’s-sized helmet fits on a kid has a lot to do with the chin strap length, too, and on an adult helmet the straps are longer to accommodate an adult’s longer face structure. You would have to tighten the straps to a point where they are rendered useless from a safety perspective.
Focus on fun with a dash of safety when you’re working with getting your kids on bikes. It’s their first taste of wheeled freedom, and it’ll stay with them for the rest of their lives. Don’t make the mistake of “you’ll grow into it” – that will stay with them for the rest of their lives, too.
[Edited 16 July 2020: One caveat for getting a bike that’s a little “too big” for a kid is that if they are a confident, capable rider, it won’t be an issue for them – but don’t go too big; this can especially be the case for 10/11 year olds and up as legs and torsos lengthen at a rapid pace. Two Wheeling Tots has a FANTASTIC overview of different bike types and how they can be like comparing apples to oranges.]