One to one transfer is made more challenging with the use of a baster for transfer.
Opaque containers with tops.
Here the containers are of very different sizes and a funnel makes pouring a little more challenging.
When introducing this type of work always start with clear containers, colored water, and one to one transfer and progress to more challenging opaque containers, clear water, and one to many containers.
TIP: Coloring water with food coloring emphasizes he level of water in each container. Colored water spills are also easier to spot on the table or floor for clean up.