Blend spinach, cheddar cheese, cream cheese, and cumin in a food processor or blender until smooth, scraping down the sides as needed.

Spread a thin layer of the spinach mixture onto two slices of bread, then place the remaining bread slices on top to form sandwiches; lightly butter the outsides of each sandwich.

Warm a skillet over medium heat and cook each sandwich for 2-3 minutes per side until warmed through and the cheese is melty.

Serve the cooked sandwiches warm, cut into convenient slices or cubes for toddlers.

Store any leftover spinach mixture in an airtight container in the fridge for 3-5 days to prepare additional sandwiches later.