help! has anyone got the sew your own sewing book?

[AnyaKnowIt]

I want to make the girls dress on page 213. In the book the ages go from 3 years up to 6. Bit on the paper patterns the sizes are 3-6, 6-9, 9-12 then 12-18. Which look like ages in months to me.

So is it me reading it wrong or is it the book.

Thanks.