Have them record how long it takes an ice cube to melt at different points during the day. Record air temperature and length of melting time, and have them predict what the melting time would be at a certain temperature. Then, wait until it is that temperature and see if you’re right! (To make it more complicated, include shade/sun variables or put the ice cube on different surfaces to see if the color or material matters.)
Mail letters/postcards to friends and family in different states (or countries). Predict how long it will take to get there. Track the length of time it takes to get there by asking people in the letter to send you a message by email/text as soon as they receive it. For an added bonus, try sending something to both an APO and physical address. We did this with my brother in Germany – it was worth the extra postage to see which way took longer. You can also try sending a postcard and letter to the same address to see what takes longer. When we did this, we found that there was a slight correlation in miles vs. time, but the letter we sent to Anchorage was received faster than the letter we sent to a rural town in our state of Minnesota!
Choose five unrelated words, and have your kids create stories that use all five words.
Do a shape or letter scavenger hunt, looking for hidden letters or shapes in nature and architecture.
Dry ice is awesome. It’s a lot of fun, and relatively safe (other than the danger of frostbite due to its cold temperature). I’ve gotten it in shipments of frozen items a few times, but you can also buy it for just a few dollars a pound at a variety of retailers (20 in my local area). There are a lot of science experiments that can be done, but mostly we use it to quickly experiment with freezing times, and talking about what boiling means and why some liquids can boil at room temperature. Dryiceideas.com is a good place to get ideas and safety tips and find retailers.
These are just a few ideas to get you started!