I am not an orthodontist, I'm a general dentist. An orthodontist has completed a postgraduate degree in order to register as a specialist, their area of expertise is in correcting poorly aligned teeth. However, part of my job as a general dentist is knowing when is the right time to refer a patient to an orthodontist. I find that a lot of parents are surprised when I tell them it may be worth sending their 7 year old for a consultation. They have a fixed idea that orthodontics means braces, and braces mean teenagers.
There are definitely benefits to early referrals in certain cases, as early intervention can mean easier treatment as a teenager, and sometimes avoiding braces or even surgery later on. For example...
Space maintenance
In my article about baby teeth, I explained the role of baby teeth in holding the space open for the permanent teeth that replace them. If a critical baby tooth is lost early for some reason, (usually due to being knocked out, or extracted because of decay), an orthodontist can fit a wire to keep the space open until the permanent tooth comes through.
Anti-habit devices
Some kids have a thumb or finger sucking habit they just can't kick. When it continues on after the upper permanent teeth have erupted at around 6-7 years old, it can cause the teeth to be misaligned. One way to deal with it is to put a semi-permanent plate in that reminds them to take their thumb out and stops them from being able to get suction. It's usually a curvy wire cemented in place that sits behind the upper front teeth.
Growth modification
Sometimes the cause of crooked teeth is actually a discrepancy between the size of the jaws and the teeth. A big upper jaw and/or small lower jaw causes that buck-toothed look. A small upper jaw and/or big lower jaw creates an underbite, where the lower front teeth are in front of the upper front teeth. A narrow jaw bone can mean there's not enough room for all the adult teeth, resulting in a cross bite or crowded teeth.
If a problem like this is diagnosed early, an orthodontist may be able to fit a plate to help guide the growth of the jaws to create a more favourable jaw relationship. These are known as functional appliances. Once a child is in their teens, it's too late as there is not enough growing left to do.
Early intervention isn't always the answer, it really depends on what sort of orthodontic problem your child is facing. Sometimes early treatment won't completely solve their issue, and further treatment will still be needed as a teenager. It's worth considering though, even if an orthodontist recommends simply monitoring your child's growth and development for a few years.