Onigiri (rice balls) are probably one of my kids' favorite lunch or snack foods, and definitely one of the easiest to make! I usually use whatever rice is leftover from dinner, add a little sushi vinegar, and voila - rice for onigiri. :)
Besides the rice, you can use whatever filling you like (if you want any filling at all) - many people use a little tuna or smoked salmon mixed with mayonnaise, or some dried fish flakes (bonito) mixed with a little soy sauce, chopped sour plum (umeboshi)... the possibilities are endless.
Making onigiri is deceptively simple. I use a sandwich-sized ziploc baggie and put a little rice in one of the corners and squish it down, making an indentation in the center. Put whatever fillings you like in the indentation, add some more rice over the top, and squish that onto the already squished rice. That's it! You now have totally kawaii little balls of goodness for your munchkins to munch on! I often make a simple bento with onigiri, sliced veggies and fruits, and some leftover meat (teriyaki chicken or what have you) - both healthy and ridiculously easy, and the kids all love them.
As a side note, these do NOT refrigerate well - though you can freeze them. I have heard that microwaving a frozen onigiri for a minute or so makes them warm and tasty, though I have not tried this yet. If you have experience freezing onigiri, please let us know - busy moms love freezer food! LOL
