Here is a list of most common brands of Brazilian jiujitsu Gis and a little snippet on the advantages of each Gi, hope it help parents choose the best for their kids.

Be careful when purchasing uniforms of the size, indeed there is a size chart must be included with each purchase, for example a fat kid his weight and length are 5'6 260lb Probably, A2 is little bit short for him, then he may purchase A3 and for sure he will get comfortable with it.

Beware of washing and drying: It is a long-life cloths but be careful of machine dry, just hang dry.

After choosing your child's BJJ class go and purchase a uniform for hem/her.

Brazilian jiu-jitsu gi is different than other karate gi and cannot worn instead of each others.
BJJ Gis are much thicker, especially the lapel. In addition to getting torn easier, your karate gi would also make any choke much worst, and give you a nasty case of Gi burn.

The cloth is also different, which can cause some serious friction burns, provided it even lives up to hold it's strength.

BJJ gis are very thick because BJJ is heavily based on grips on the Gi, a Karate Gi isn't meant for that, more than likely it would rip to the point of uselessness in the first class.
Read more about Karategi.

Fuji uniforms for children:
Blue Fuji Kids BJJ Uniform Gi
made of sturdy heavy weave cotton that hold up to even the most aggressive Judo & Jujitsu partners, Hence the Material is heavy gauge and sewn well.
The pants seem a bit long but it is not a problem since at this age kids grow fast it designed and come with 2 patches that can be sewn on and white belts.
Great product quality and price.

Fuji Single Weave Kids Gi - Blue color gi
Made of 100% cotton and includes jacket, pants, white belt and 2 patches which can be

Fuji Gis

sewn on, mid-weight gi comes with strong pants, special reinforcements and features a true BJJ cut with a shorter jacket and tapered arms. sizes chart for this Gi is: C00(3' 9" - 4' 0"), C0(4' 0" - 4' 3"), C1(4' 3" - 4' 6"), C2(4' 6" - 4' 9"), C3(4' 9" - 5' 0").

Fuji BJJ Pink Blossom Kids Gi
It is build for girls gi uniform.
Pre-shrunk for minimum shrinkage.

Fuji Single Weave Kids Gi - Pink color gi
It is very comfortable and fits all ages by view your age size in size chart delivered with the gi kit, the pink color make it is suitable for girls than boys.

The brand Tatami Estilo Kids BJJ Gi unifroms:
Set is designed with a Style for children BJJ GI for young boy and girl who is looking for high quality with sophisticated style and detail. It is constructed on the pattern of GI children using only the best quality materials and is a must for any up-and-coming star. Special features - 425gsm single piece of armor vest high-tech - necklace of rubber-coated cotton helps to sweat absorption - contrast stitching - designs debug new - area knee strengthened - stitched across all stress points triple - cotton pants are 8OZ light weight, and triple-stitched with more layers coiled - elastic belt for waist with drawstring.

Tatami Estilo Kids BJJ Gi
Black color and White, ina ddition to blue Tatami Estilo Kids BJJ Gi.
Comes in size M0.
These outfits are designed to give child a solemnly look like great fighters of jiu-Jitsu.

The brand Baby Grappling
Baby Gi 3-piece Miniature Martial Arts Play Set - Size 80, 12/18M Red by Baby grappling.
maintain the shape of a kimono and stop