Build a simple pattern of colored blocks in front of your child, such as: red-blue-red-blue, or a tower of 3 blocks in a specific color order, and leave it as a fixed model in front of them.
Give your child a matching set of blocks and ask them to build the exact same pattern next to the model, comparing it to the model step by step to make sure it matches.
Start with short patterns of 2-3 blocks, then gradually increase the complexity (a repeating pattern of 4-5 blocks, or a pattern by shape instead of color). This activity strengthens visual observation and short-term memory, and prepares the child to understand mathematical and logical patterns later in school.