Splitsville really is a regular restaurant similar to an Applebee's, Chili's, or Red Robin. The bowling lanes are on the second level so if you don't go up the escalators, you'd never know there was bowling. They have a wide-ranging menu and there is even a sushi bar - the sushi was very good!
To me, Splitsville is a great choice. We ate while we bowled and would definitely eat there again, whether bowling or not. Not sure, however, about the escalator issue, as we bowled downstairs (i.e., the level of the front door). There are probably eight lanes down there, if I had to guess, so I'm not sure you can actually avoid seeing the lanes on either floor. If you think the bowling would be fun for the kids, you have access to the full restaurant menu while bowling, and there is a table at each lane to use for that purpose. On the flip side, if you don't really want to bowl and fear that the kiddos would potentially pitch a fit at being there and seeing others bowling while they can't, then maybe look elsewhere.
Among the options you're listing (Trex, RC and PH), I'd probably go with Trex. We've been pretty disappointed in RC the last couple of times we went (always willing to give a second chance, but unlikely a third at this point). Has been a while since we hit Trex, but I remember our kids enjoying digging up dinosaur bones in the sandbox while we waited for a table, and the food was OK (but same company as RC, so likely very similar food...I've just forgotten or blocked it out - ha!). As for PH, we enjoy it enough, but Trex would likely be more appreciated by younger kids like it sounds like you have.
If willing to branch out, I'd support Earl of Sandwich (our kids love it, and there are definitely available options for picky kids) or the Wolfgang Puck options or, if willing to go with quick service, the new BBQ place at House of Blues or Cookes of Dublin....or the Food Truck park that is now open. One of the trucks has the potato and kielbasa pierogies from Food & Wine...and corn dogs.
In short, there are plenty of good lunch options at DTD. (For the record, we also liked the movie theater option, where we saw Frozen when it came out, but definitely would be a tough challenge with a 20-month old!)