ANSWER

6-7 year olds

a)    The first figure has 9 buttons on the border and 4 inside. The second figure has 20 buttons on the border and 4 inside.

b)    The next figure has 25 buttons ont the border and 5 inside.

For question c, there are many answers. Here are two of them. The first one has 24 buttons on the border. The second one has 26 buttons on the border.