Hello travelwithkids,
We have been on the road with our kids for quite some time. Our kids are 3 and 6 years old now and we are in Mexico. When we are cycling the children tend to be very relaxed and don't really need toys. They sit quietly or talk with us or sing. Our 3 year old sometimes plays with her 2 dolls.
For the time off the bike we have some drawing and crafts materials like paper, tape, crayons, glue, etc. This is mostly used in the tent when it is too cold or raining outside, or when there are too many mosquitoes.  We also carry a few toy cars, some lego, a pocket knife, a sling shot and some rope. Chalk to draw on the street is a must. A little bucket and a shovel can be nice.
 In case of emergency we have a movie or two on our tablet and we have a lot of children's books on the e-reader.
But most of the time the children don't play with ther toys. They are incredibly creative with what they find in nature.
You can read more about us on thecyclingfamily.com
We might be in South America too when you are there.