MSP- Lunch near Como Zoo
There is a cute coffee shop called Java Train in the Como neighborhood (I think it's on Pascal) very close to the zoo. They do panini sandwiches, soups and also serve Izzy's ice cream (the best!). Depending on how old your grandson is, he could play on/around the train-themed toys and climbing apparatus both inside and outside (this is a very kid-friendly place).
Snuffy's is not at all remarkable.
Maverick's is the real deal, and they have a singing deer, a source of fascination for some grandson types. There's no pretense, just sandwiches like sandwiches used to be. That said there are some sandwich religion places too, just not in zoo neighborhood.
If you're open to dining picnic-style, do what my family often does: Grab sandwiches at Nelson's Cheese Factory (at the intersection of Snelling and Como) and bring them to the park with you. Reliable, far better-than-average hot and cold sandwiches just a few blocks from the park.
However, if your zoo trip coincides with the state fair, Nelson's is out of the question - it's ground zero for fair traffic.
Nelson Cheese & Deli - duplicate
1562 Como Ave, St Paul, MN
Key's Cafe (Roseville) is very kid friendly and has decent food - it's pretty good in a small-town-cafe kind of way. My favorites are the turkey dinner and the cold meatloaf sandwich.
Snuffy's Malt Shop is OK for burgers and fries (and malts) - I don't really like the place, but others do.
Maverick's is a board favorite for roast beef sandwiches - fast food the way Arby's ought to be but isn't.
China Jen is at 2193 Snelling Ave N, almost at Hwy 35. It's very casual with good Chinese food. (I think - I haven't been there for a long time.)
A bit further is University Avenue, with tons of casual Asian restaurants. I like Hoa Bien a lot these days, but see these threads for many more ideas (not all are on Univ Ave, though):
And here's a thread on dining near the St Paul campus of the U of M, which is relatively close to the zoo:
Have a great outing with your grandson!