Children reach developmental milestones at their own pace. Minor, temporary delays are usually no cause for alarm, but an ongoing delay or multiple delays in reaching milestones can lead to issues later in life.
Fun idea: If you don't pick something up after one warning, mom confiscates it and puts it in a "Ransom Rubbage" box. The only way you can get it back is to draw a task from the envelope attached to the box lid. Some tasks are hilarious!