Mom61, I hope you enjoy your trip to Hiroshima.
As far as food goes Jonathans has omlettes, hamburgers, steak, baked chicken and rice with garlic sauce. That kid of thing. They are not expensive, and have a drink bar in them.
Gusto is probably the best option for a family. They have vegetarian options, good salads, healthy options. They also do great kids meals, though they are not vegi.
There are also the usual plethora of the dreaded McDonalds, subways and cold stone ice cream cafes. That was all I could eat or order when I first came to Japan! You will also find a LOT of starbucks if you need a coffee!
Banyan is also a good family Chinese restuarant chain, and has healthier options.
All these family restaurants have photos of the food in the menu, so you should be able to order without difficulty. They are probably about 1000 yenper adult, and kids meals (including a gluten and low allergy option in Gusto at least) are about 450 yen.
If you want to try more Japanese food, there are some lovely places. Not all raw fish if you are not keen, though if ou like sushi and sashimi of course you will find wonderful food. If you can get a Japanese speaker to go with you, you might find you enjoy a good Japanese restaurant. I adore the crab meat steamed over rice, with little dishes of spinach and sesame, steamed savory egg custard, miso soup with seaweed. I think these places will be quite difficult without a Japanese speaker. If you get the chance to go, it is worthwhile. The food in Japan is generally excellent.
Japan is VERY clean. I have never been to a place which is dirty here. I would not worry about eating out at all.
If you and the children eat meat, I would also reccommend Bikuri donkey, which has great hamburgers and a lovely atmosphere.
I rather like ramen, noodles in soup. Ramen are very good and tend to be inexpensive, though the counter style service is hard with children.
I hope you have a good time!