Furikake seasoning ふりかけ is the mixed seasoning used for this very purpose. It is very popular even in the U.S., and many different varieties are available; some are made specifically for kids and some are for adults. I even know somebody who uses furikake to season cottage cheese (Could that somebody possibly be my wife?). I made the big mistake, early in our marriage, of showing my wife, the way I used to eat rice when I was a kid. I just added a pat of butter to hot rice, let the butter melt first and then mixed in soy sauce as seen below. It had been a long time since I had rice that way. My wife immediately took a liking to it and this is her favorite way of eating fresh, piping hot, white rice. In horror at what I had unleashed I had to warn her about the impropriety of enthusiastically putting together her "favorite" rice at a restaurant. While eating rice for dinner at my mother's house in Sapporo, I reminded my mother of how she used to serve butter and soy sauce rice to me as a kid and how I had made the mistake of introducing my wife to the dish. My mother abruptly put down her chopsticks, got the butter out of the refrigerator, distributed it all around followed by the soy sauce. While mixing the ingredients into her rice she mentioned she used to eat her rice like that as a kid but hadn't eaten it in a long time. She took a bite, sighed and said it sure was good!
It is always a bit iffy to season plain white rice in public by doing such things as pouring soy sauce, broth or simmering sauce from, say simmered fish 煮 魚 or miso soup over the rice. But many Japanese will do exactly that in private. If I pour miso soup over my rice, I would call it にゃんこめし meaning "cat rice" but, for people from other regions of Japan, "cat rice" is rice topped with bonio flakes and soy sauce and, they may call it "nekomanma" ねこまんま (the meaning is the same, i.e., "cat rice"). The fact that there is a specific name for this type of rice (albeit a bit derogatory) indicates many Japanese are eating rice in this (unacceptable) manner. I do not recommend doing this in public, however. Why such doctoring of rice is frowned upon by Japanese is "not logical" as Mr. Spock would say. After all, many donburi どんぶり dishes are made using rice in a seasoned broth with toppings and dishes called hiyajiru 冷や汁 and ochazuke お茶漬け are indeed rice in a broth. It appears that as long as it is prepared in the kitchen or is meant to be consumed this way, it is a "legitimate" dish and can be eaten in public. But if you improvise at the table by pouring soup over rice, it is not OK; go figure. I think there was a lengthy discussion on this subject (in Japanese).nori "ajitsuke (yaki) nori" 味付け(焼き)海苔 which was my favorite way of eating rice as a kid (and even now). I am not responsible if you find the comforting flavor of this dish addicting.