If you are unsure of which size to get your child, I will recommend what size I think based off real-world use. The size 3 is good for any child until about first grade or second grade, which is when a child should move into a size 4. The size 4 should last until they get to middle school (around 6th or 7th grade), and then they would move into the adult official size 5.
This is a very special soccer ball which I’ll think you’ll fall in love with. At least that was the case with me. I must say that I don’t normally trust new comers in the industry of soccer equipment. I mostly prefer established companies like Adidas, Select or Brine. However, the guys at Bend-it (the company behind Kunckle-it) really changed my perspective.
The soccer ball has gone through various changes just as the football game. As opposed to yesterday’s football ball that had stitches and seams and the classic black and white design, today’s soccer balls are designed with the latest technology that lets the ball bend more, fly quicker and also dip harder. Besides, they are quite soft that they let players kick the ball further without risking injuries. https://www.youtube.com/watch?v=DGp37du0xbQ