Online srabble: 

Play to your heart’s content when you should be writing an essay and learn two things about language acquisition: (1) we continue to acquire new words throughout the lifespan and (2) we can learn and use words without any idea what they mean or even what grammatical category they belong to. Try vly, euoi and zati for size – all English words.

Tips on vocabulary learning:

A commercial site, but here they offer you ten free tips on how to improve your vocabulary. Does the young child use any of these methods? Do you? What are the differences between child and adult word learning?

Wordbank: 

An open database on children’s vocabulary growth, which contains data on more than 60,000 children across 21 languages. You can explore a wealth of data profiles and analyze or even use free software to do your own investigations (see also Frank, Braginsky, Yurovsky & Marchman, in press).