Dad wants his son to do traditional boy things (suggested by the ball/bat/truck toys he’s holding). The little boy obviously has some gender jealousy/disphoria (not sure about correct terminology) as suggested by the hair style, pink clothing, and(?) hopscotch.

The joke is that so many kids were told this type of thing growing up ‘you can do/be anything you want to be,’ but many/most of them wouldn’t be accepting of this type of behavior/choices.

‘You can be anything you want to be (except a transgender/girl).’