Three year olds like...
Give them different materials to encourage drawing and scribbling, including chalk, pencils, crayons, markers, finger paints.
Use descriptive words such as colours and opposites (hot/cold, big/little, fast/slow) as well as action words (flying, splashing, running) when you are talking with them.
Give them extra time to share their ideas.
Give them choices - about what foods to eat, toys to play with, clothes to wear. Model correct sounds and grammar for them - child says "he wunned" and you say "yes, he ran".
Read books that are predictable and repetitive - pause to give the child a chance to fill in the words and phrases.
Play and pretend with them! They may like acting out scenes from their favourite videos, pretending to eat in a restaurant or to be a teacher or firefighter.