Melbourne

Ah cool. I've never done potluck really outside of making a simple cake to bring and don't have kids, but if I think about the logistics... hmm.

Mini fruit tarts caaan be made a day ahead to go straight in an esky on departure... However they are fussy to make, fragile and need to stay chilled due to the custard filling when fridge space at the host's may already be at capacity. Same goes for mini pavs. A choc ripple cake is very easy but with the cream and delicate structure I don't know how well it'd survive heat or bumps. Snot blocks are a bit large.

Pudding cups and frogs in a pond (clear plastic cups of lime jelly with a Freddo in) are a bit sturdier but still probably need to stay chilled if they don't go fast. Depending on weather. And they're dessert items.

Cake pops can be made with a bought cake and a tub of premade "frosting" (the thick fatty Betty Crocker stuff). The "candy melt" coating would make them sturdier to knocks. They don't need refrigeration (if you don't use things like cream cheese) but would be time consuming to make individually and run out very fast. Also safety concerns if the kids are young enough to bite into splintery wooden sticks or swallow a piece of hard sugar shell. Pain in the butt.

Pinwheel sandwiches rock for presentation but be mindful of fillings. Many contain cream cheese which should be thick enough to hold them without a fixing toothpick (unsafe) but if that's the case refrigeration applies. Using peanut butter or Nutella is better for food safety but raises the whole nut allergy thing. Hummus can upset tummies that aren't used to it.

Cupcakes or biscuits seem like a a safe bet. Mini cupcakes or biscuits would go further when distributed and lessen the risk of filling up before the real food/spewing. Also consider those baked ham and cheese rolls, Vegemite scrolls or cinnamon scrolls. Lamington fingers. All of this stuff has the advantage that it can be shop bought.

Also this depends on the number of kids but consider the little gingerbread Pfeffernusse if you see them.

Edit: Dude. The answer was obvious. Chocolate crackles