While we'd expect such toys to be included for free as part of a Happy Meal, they're actually offered as a standalone set (with six plush toys, 4 limited-edition food coupons, and a Hello Kitty picnic bag for $288HK [~37.12US]). You can also get the six main toys, which look like Hello Kitty dressed as various Sanrio character-fruit hybrids, for about $2.58 US with any food purchase of $2.32 US (which seems much preferable to some customers buying a Happy Meal for the toy and tossing the food during especially popular toy promos here in the US).
There are also four other toys that can only be acquired through more specialized means. Two come come free with the purchase of a set of McCafe drink vouchers:
The last two can only be collected from ordering McDelivery (McDonald's delivery service in the territory):
The promo is not just toys though; there's also a selection of food items with themed-packaging for the occasion:
While these are only currenty available from McDonald's in Hong Kong, if you're a huge Sanrio fan, they're also up on eBay at varying price points.
Images via McDonald's Hong Kong.