It has a more "adult" world
Around the age of 19 months, your toddler begins to understand when things do not conform to adult ideas. He laughs at what is obviously wrong, like calling a giraffe a zebra, a brother or a sister. He also notices things - a teddy bear with a missing eye or a new stain on the carpet.
His vocabulary is growing rich
Even if you do not understand that half, at most, of what your toddler says, he begins to understand most words you use in his presence. His vocabulary is growing and he becomes able to associate words like "Me go" or "You, put" ...
It becomes authoritarian and seeks to negotiate
To limit the power struggles when your toddler looks for its independence, make sure you treat him as you would like us to treat you. Prefer compromise orders. Instead of: "You can not get out now", rather say: "We read a book together and go after." Instead of ordering him: "You must put these cubes before dinner", imagine a game: "I pick up the pieces while you take care of cubes."
He loves contact
The game is enough to stimulate your toddler. So avoid the theoretical lessons until the age of 3 years at least. The park or at home, encourage your child's contacts with other children, but you expect them to play together at this age.