"Any other foodie tips welcome."
There is a Japanese restaurant review site called Tabelog that is well worth looking at (it's available in English).
It has reviews for everything from fine dining places to hole-in-the-wall type places.
For example, @InvalidUserID mentioned "there’s a really good tonkatsu restaurant called Hirata Bokujo just around/inside the east exit to the station."
Hirata Bokujo appears to be a small chain and this is the page with the reviews (and photos of the food etc) of the location next to Yamagata station:
https://tabelog.com/en/yamagata/A0601/A060101/6005167/
Apparently, it's the 7th highest rated tonkatsu restaurant in Yamagata (out of 52).
You can look broadly at different areas or just restrict the area you're searching in to a particular distance from a train station etc and you can also search by type of food etc. It also shows on a map where the restaurants are.
.
"... we're not real foodies either (also catering for kids)"
Tabelog is great for that as well. For example, here is a list of 638 pizza restaurants in Osaka ranked by reviews
https://tabelog.com/en/osaka/rstLst/pizza/?SrtT=rt
Or you can narrow it down to 325 pizza restaurants in central Osaka:
https://tabelog.com/en/osaka/A2701/rstLst/pizza/?SrtT=rt
Or you can narrow it down even further. For example, if you were staying at the Holiday Inn Express in Osaka then the nearest station is Hommachi and here are five pizza restaurants within 500m (there are 21 within 800m):
https://tabelog.com/en/osaka/A2701/A270106/R9135/rstLst/pizza/?SrtT=rt&LstRange=SG
Tabelog can be very useful indeed for finding somewhere to eat.