Here I will show you and easy way of making your crocheted (or knitted) toy into a rattle for a baby. I have found that if you use bells, you need to put them inside some kind of container. If you put the bell(s) directly into your toy, the stuffing will muffle the sound a lot and the jingling disappears.. I have used the yellow plastic containers that you get in milk chocolate eggs (f. ex. Kinder-eggs), those are just the right size. Just put one or two bells inside and close it up :) If you want your toy to be washable, you should make sure that all openings are sealed. Use tape or glue to seal the container.
Now, if you have a container but no bells, you can just as well use dried peas or small pebbles of stone or beads. Just make sure the container is completely sealed, because if the peas get wet, the result may not be too pleasant :p
Hope this was helpful, feel free to contact me with questions :)