Ooh pattern blocks! My kids love these, a few of us tried using them for sorting activities and it's such a simple way to teach shapes without it feeling like "learning," lah. You can use anything from tupperware to mug carts, even just pile them on the floor honestly haha. The best part is they'll play with the colours and shapes naturally, and before you know it they're recognizing sides and corners without you having to drill it into them.