OMG, I play with my older daughter to I spy a Yellow car too! and I thought I invented the game, lol.
Only that in our case, the game last for about a month and I lose horrible, something like 6 against 30, but it was no fair because I was driving and needed to put attention, lol.
The other game we play is talk without a common later like "s", we love that game, we just talk and try to ask question to the other so they say the later.
And also we play "Basta" (but only when husband drives), we take some paper and divide it into sections with:
Name, Food, Animal, Thing, and can be what ever you want, state or city, Spanish word or what ever you think your kids can do.
Then one of us start thinking the ABC's and the other decide when to stop saying "Basta", what ever is the letter that the person says is what we have to find words that start with that letter for each of the sections.
When somebody finish says "Basta" and all stop writing, and you repeat as many times you want, 5, 10, etc. wins who get more points, each word is a point.
Another similar but you don't need to write is to pick a letter and take turns saying all the animals or food or whatever that start with that letter, if you can't think in nothing in 5 sec. you are out.
Hope you have fun.