If they can make shortcrust pastry, they can easily make all sorts of yummy things including quiche and tarts. Shortcrust is a a fun and reasonably easy pastry to make with toddlers. If you have a very young toddler or short on time, you can buy it ready-made or make it yourself. But I definitely recommend giving it a try. As I hope is obvious from this video of my 3 year old, pastry-making is a lot of sticky, hands-on fun; great for developing those motor skills.
As toddler concentration spans aren't long and this isn't a quick process, I usually make the pastry on one day and then do the quiche or tart with them on another. It will keep wrapped or covered in the fridge for a couple of days. You can also freeze shortcrust. I'll let my youngest chef take over...
I haven't included quantities because shortcrust pastry recipes are everywhere and how much you need will depend on what you're making. My only advice would be don't get them to make too much in one batch because it will take them ages to rub the butter in and they could loose interest; about 150g-200g of shortcrust is a good amount.
What next? Some ideas of what to make with shortcrust:
You use exactly the same technique when making dough for scones and for crumble toppings. So once they've mastered 'tickle fingers,' the recipe options are numerous.