One of the seats is missing the inner valve to hold the pin in place. Another one is all marked up. None hold air very well.

Very disappointed in the size. The picture shows not only children but adults sitting on them. They are low to the ground not big like exercise ball.

I am a huge fan of the exercise balls. I love to sit on the exercise ball, and use the exercise ball as my desk chair. After sitting on an exercise ball for a few years, I can only hope, never to have to sit on an office chair as my daily chair again. I have bought quite a few exercise balls, and even use them for exercise sometimes. Lately I have been filling my small Pilates balls with sand. I was looking for other mini sized exercise balls, to make into medicine balls. My plan is to get many variable weights in the exercise balls turned into medicine balls.Upon seeing these doughnut balls, I figured I have to try them. They are small and I may use these balls in exercise situations. But my primary thought is to fill some of these balls with sand and get approximately 50lb to 75lb weights. Upon receiving the doughnut ball the first thing I noticed is the thick soft material these balls have. After purchasing many of these exercise balls, one learns they come in a great variety of materials. Some are thin, some are thicker, some are softer, some are harder. These appear to be on the better side which are soft and thick.Upon blowing these balls up they do vary in size. The variable exercise ball problem, is a problem one can encounter with all manufacturers. This problem probably has something to do with how the ball cure in the manufacturing. As the balls weigh very close to each other. Anyway, based on previous reviews I was expecting these balls to vary in size, and the variable sizes, is part of the reason I wanted this set. If I fill these balls up with sand, I will get different weights for different sizes. So unless one needs just a single size, variable sizes could actually be an advantage. To get to the max size of these balls, one usually has to fill up the ball, waited a day, put some more air into the ball, and they will have to add more air a day or two after that. As the rubber stretches a bit for the first day or two. So my estimate range of sizes which I received, without expanding the doughnut balls to their fullest comfortable level is about 14 to 16 inches wide, and 7 1/2 to 8 1/2 inches high.As a chair these balls will work for a toddler. A 4 to 7-year-old child will probably be comfortable sitting on the ball as a chair. An older child and adult could be very comfortable sitting on the ball as floor cushion. So if one likes to sit on the floor cross-legged, this doughnut ball works very well as a bolster. One can use the doughnut ball as a chair bolster. Many times couches and chairs are very low, this ball would raise the height by 7 to 8 inches. 7 to 8 inches may be too high for some situations but works for others. Using this doughnut ball as an exercise ball does not have many uses, but has uses. It is very hard to stand on this doughnut ball, so for standing/ jumping exercises a Bosu ball is better. But this doughnut ball is good for abdominal work, leg bolster, and a slightly unstable pushup surface.Overall, this ball is a great product, which fits a specialty market. I added one ball to my couch, making my couch a more therapeutic height for me to sit on. Optimally one’s thighs should be parallel to the ground while sitting. I also slightly under filled one of the smaller balls with 45 pounds of sand, making one of these balls my favorite additional weight. Lifting this sand filled doughnut ball is actually quiet fun. There are multiple grips one can grab this doughnut ball with, and the ball is soft. For heavier weights I may prefer the doughnut shape over the ball shape. Just know that trying to catch a doughnut shaped medicine ball is a little dangerous, as the odd shape can easily hurt a finger. So no throwing doughnut medicine ball, although one can hold the ball from the center hole and do a spin toss and catch.One more thing if you're curious how to fill these doughnut balls up with sand, I’ll tell you. 1st one needs to sift sand to get out any small rocks, and make sure the sand is flowing smoothly with no clumping. 2nd, they will need a funnel end or a tube end which fits into the ball. The funnel end outside diameter should be about 6mm.  3rd, the larger the bucket they have emptying sand into the hose that attaches to the ball, the less they have to refill the funnel. From here place the bucket in a higher position than the ball, insert the funnel tip into the ball, and fill up the bucket with the sifted sand.

These are much smaller than pictured. 2L bottle to show scale. Not a big problem for me since I intend to use with 6-7 year olds. Also, they are hard to fill completely. The holes don’t have a valve so as soon as you get it full-ish the pressure forces the pump nozzle away and out of the seat. Even with help to try and keep it inserted and to replace the plug quickly, they lose enough air to have creases and not look full. But the worst thing for me - these are NOT the same size as each other! I filled the top one in the picture as full as possible, with help. The bottom one I filled alone and it has a lot of give. And it’s clearly larger. The others are similarly irregular. When I stack them to store them, it irritates the part of my brain that craves symmetry.

I love these for sitting Aron’s my coffee table for playing games. No one will play games anymore because I have stupid teenagers but some day (not too too soon) I’ll have grandchildren that love me.

Product is much smaller than it appears in the picture with the child. Would work well as a seat cushion.

So I purchased these for my classroom for a different and flexible seating option. They were a little smaller than I imagined but I think they will be just fine for 13 year olds. I sat on one myself and they hold weight and shape just fine! Excited to use them!