ditto. I believe it is impossible to be proficient and eloquent in more than one language at a time.
And even without that, my vocabulary has huge gaps. Why would a ten year old need to know the word for "rent"? I didn't learn it until several years ago, in my 40s.
But I disagree about eloquence. We're just out of practice. If we spent six months of the year in Moscow and six in New York, we'd both be perfectly fluent in both.