I was fixing some toys of my 5 year old and he asked me if he could watch the glue dry... I told him "son, that's like watching grass grow π"... his reaction, "really π±... can I go in the backyard?", me "yeah, sure, I guess π€¦ π".
He's still there... sitting on the ground, watching... asking every 2 minutes if the grass is any taller π€£.
Go out every day with a ruler or a tape measure and take a picture with a measurement. He might not notice or remember the daily growth but after a a few weeks there should be a noticable difference if the climate of your area is still warm enough.