Start with two clear groups
Put a few safe objects into two groups, such as toys and clothes or fruit and animals. Keep the rule visible and easy to change.
Make a tiny repeating pattern
Place two objects in an AB pattern, then pause before the next place. Invite your child to choose what comes next and show the pattern with blocks or movements.
Let the child explain the rule
Ask what belongs together or how the pattern works. A pointing gesture, a word or a new example can all show the idea; there is no need to finish a long row.