Hello, welcome and congratulations on the new baby!
I don’t have any children so take my information as that - information, not personal experience as anything but the world’s best babysitter!
How many people are in your family that will be riding in the van? There are a lot of van life families (with infants and toddlers) on YouTube. I think that would be your best resource, especially visually. And you can ask the very people whose videos and set up you like the most.
European vans commonly have a full bench in the front seat, so if you can find a van with that option, my opinion is that that would be ideal. Behind the front seat, it’s not uncommon to find another bench seat or even a single or double seat/bench. To find out if those are even options, your best bet is likely with contacting Sprinter/Transit/ProMaster dealerships. That way, you can still buy a used one from a private owner, knowing that the option is at least available.
Again, welcome! It’s great to have you here! Feel free to look around and ask any and all questions that you have!