I think the sams diner kitchen is still there, just the front covered over like you said.
Really, you could move maybe carousel and tweety cages up into that area around sams diner / front of road runner, then you would have a ton of room, but honestly, moving carousel probably isn't that great a gain as its kind of tucked back in the corner. Though I think a carousel is a ride that should really be completely visible from the center of the area. Like, if it was about where the big tree is. They always have great visual appeal for kids with all the light and sound, should be able to see it clear as day as soon as you look in the direction on kids wb from the plaza.
If you moved tweety cages up to that sams diner area, you would still have room for another flat (replacement drop tower?) where the rest of the seating is.
The thing is, it's an area that really should have a food outlet, not just a random food van or mobile trolley like it has been reduced to. Especially if you have more kid friendly options available. The more I think of it the more it seems like it just needs a complete, shut it down for 12 months, knock it all down kind of rebuild. Looking at the sat images, id even say it would be worth re-aligning the back road and changing the first stunt show entry damp/driveway to gain another 10m+ depth to the kids area at the back. Even maybe absorb the first aid area (temp relocate it to stars?) and toilet block and just start with a new layout that is all designed to fit together, rather than create pockets of dead space.
Food outlet and seating, 4-5 new rides, id even go so far as to maybe suggest returning a low stage for a kids show to return. Would also give somewhere permanent for toons character photos that is well themed with an actual background instead of just using the tree with random people in the background. Idea of a decent playground is awesome too as they are pretty space efficient given you can build up, not just out. Makes an obvious tie in with the parents area nearby too.
If im honest as a parent, I really dont care about gardens that much. Id actually put a covered area well ahead of gardens and see it as a massive plus. It's honestly probably not a consideration cost wise, but if they built a new part of the kids area that was under covered (either main street roof style or even just a regular metal roof kind of like a carport) it would be a great place to hide out the bad weather and still keep the kids amused. May mean they could utilise every square inch of space too instead of losing 1/3rd to greenery.
Maybe kind of build it a bit more like an arcade/ boardwalk with a few of your ride options, the food outlet, parents room and a playground under it. Would be a lot less dummy spits and wet bottoms from my kids if we had some sort of option like that.