Make hot ice (sodium acetate trihydrate)

What can we use if we can't find white vinegar, baking soda, or a heatproof glass jar?

Use any clear 5% distilled white vinegar for the 'Measure 2 cups of white vinegar' step and regular table baking soda (sodium bicarbonate) for the 'add 1 teaspoon of baking soda' step, and if you don't have a heatproof glass jar you can pour the hot concentrated solution into a Pyrex measuring cup or other heatproof glass/ceramic container.

My solution formed crystals while boiling or stayed cloudy—what should we do?

If crystals form during boiling or the liquid isn't clear, reheat the solution until the crystals dissolve and then repeat the cooling step while keeping the mixture at a gentle simmer and reducing it to about 1/4 of the starting volume as instructed.

How can we adapt this activity for younger kids or older kids?

For younger children have an adult handle the 'set the saucepan on medium heat', 'pour the hot concentrated solution into the clean heatproof glass jar', and 'use oven mitts', while the child measures the 2 cups, watches crystallization, drops the seed crystal, and takes the photo; for older kids let them add the baking soda 1 teaspoon at a time, control the simmer to reduce to 1/4 volume, and troubleshoot reheating crystals with supervision.

How can we extend or personalize the hot ice experiment after it works?

Try adding a small drop of food coloring to the concentrated solution before cooling, grow a seed crystal on a string or use silicone molds to shape the activated 'hot ice', and make a time-lapse or photo to share your finished creation on DIY.org as the final step.