Here's some information about what clothing you are going to need

 

Crash Helmet There's an old saying, "if you've got a £5 head buy a £5 hat". Obviously, it is most important to protect your head, and good quality headgear is certainly the way to go. Additionally, when considering headgear for a young person, weight plays an important part. Proportionally, the weight of a crash helmet puts a much greater strain on the neck of a young person, than on a full-grown adult. So light weight is essential, and the MSA insists on all Cadet drivers wearing a CMR-type lightweight helmet. Even if you decide to race outside of the auspices of the MSA, it's probably not a good decision to buy an adult-weight helmet from a motorcycle store for your youngster.
Race Suit Race apparel is made to different guidelines and regulations for specific applications. So a racing driver's suit has a requirement to be fire-proof, where a kart suit's main requirement is to be scuff and abrasion resistant. For MSA purposes, they should be embroidered, usually on the outside of the collar, with a specific designation, Level 1 or Level 2. Although some other race organisations might not be so specific, it is policy to buy a good quality suit. With the growth of your youngster quite an unpredictable process, it is also wisest not to buy the most expensive you can, just one of suitable quality, as it is likely that it will soon be grown out of!
Gloves There are many different types of gloves available to drivers, and there is little in the way of specific requirements. Suffice to say they should offer some protection to the palm, offer good grip, and have no holes in them. There are plenty of stylish designs available from major suppliers, while some drivers favour using motorcycle gloves. Certainly warm and waterproof can be an advantage on those inclement weather days.
Footwear There is not too much of a specification for footwear either, other than it should offer some ankle protection. All driving boots have very thin soles, which offer the driver maximum "feel" as the pedals are operated.
Personal Protective Equipment There are some specifics, such as neck braces and rib protectors. All a matter of personal choice, some drivers like using them, other don't. It's probably best to do a little driving first and see what feels comfortable. A neck protector can affect the comfort or fit of a helmet, using a rib protector will probably influence the seat size your driver feels most comfortable sitting in. Other comfort items are things like a waterproof over suit and galoshes. Household washing-up type gloves can be useful on those wet days, or perhaps surgical gloves under your race items. The list is endless, and very much a matter of what works for your youngster.