Usually a few months into the season they're released.
My missus bought the XS online for my lad (he's just turned 1) 2 weeks ago (to surprise me on Father's Day) she thought that would fit as it was the smallest, it would have probably been baggy on John Fleck!
I brought a toddler kit last year for my lad. thought the quality was awful, especially for the price . it was Avec rather than Nike but had no Avec logo other than a tag. The badge was a transfer and was not hard wearing at all, the shorts were just plain dark blue with no logos basically looked like a knock off you get on holiday.