Communication is a toddler skill in The Sims 4. Toddlers increase this skill by babbling to themselves, older Sims and stuffed animals, and by watching videos on the Wabbit Tablet. Happy toddlers and toddlers with the Charmer trait gain Communication skill faster.
Talking is a huge step for any Toddler. Communication skill teaches Toddlers more advanced socials. Improve it by talking with others.