There is Visual Acuity button in the right corner. What does it mean?

The visual acuity button in your Parent Menu indicates that you should perform visual acuity screening as soon as possible. It is used as a tool for tracking the progress of the visual function. Visual acuity screenings in AmblyoPlay are performed once every 2-4 weeks

If you do not wish to perform the screening right away, you simply ignore it and do it the next time. The VA button will stay there for as long as you do not perform the screening.