This is my current version of the scene where the boy jumps through the portal into the Lego world. The first part was completed in the same way as the previous scene where the boy looks through the portal, with just one difference. As my son was running, his legs could be seen coming past the portal, so to correct this I placed an empty shot of the scene over the original. I masked it to only be seen behind the portal, so the boys legs are not visible when they come through.
The Lego scene was my first effort at creating a 2.5D style scene, with lots of elements added to flesh out the image. The original stop motion element took a number of tries to get right, and to be honest, I am still not completely happy with the outcome. I used a Lego piece to give the impression of the minifigure coming down from a leap and rotoscoped it out of the final scene.
I had a number of issues with the stop motion when I played it in After Effects. Some of the camera shots were slightly blurry and the camera moved slightly at one point. I solved the camera movement by adding a Warp Stabilizer effect, which worked well. Another issue was the light changed slightly a few times, giving a flickering effect. I also managed to accidentally knock a few Lego pieces out of place. Luckily, I always make sure I take a few still shots of the scene with no character in it, so I was able to mask around the stop motion as much as possible, revealing the still shot underneath. This helped to eliminate most of the colour change and piece movement, and also masked the shots that were blurry.
I only had one road piece, so I tried duplicating it, but could not get it to work well, so I ended up masking and warping parts of the road and fitting them together to extend it. The result is not perfect, but I think is passable for such a short scene. I will have to come up with a better solution for the longer Lego scene. For other objects, such as the Lego house, I photographed them separately and either chroma keyed or rotoscoped them into the scene. I then added a blurry effect to them so they fit into the background better.
Finally, I added a background photo of a cityscape. I am undecided about how well this works, but this is more of a test for the longer scene, so I may play around with it some more before submitting.