I have anecdotally found this true as well. Toddlers and small children have a terrible working memory. It really is what's limiting their ability to count, spe

I have anecdotally found this true as well. Toddlers and small children have a terrible working memory. It really is what's limiting their ability to count, speak coherently etc. Promises often needs to be repeated to stick. Therefore they need to be made meaningful. Making promises about a banana when working memory have purged that information five minutes later just makes promising stuff pretty empty (for really small children, that is).