Enquiry on H4 Visa

Hi,

I recently transferred my H1 visa from employer A to employer B and it got approval from USCIS.

Before my transfer initiated, My wife and Kid traveled to the USA from India on H4 visa.

Now my wife and my kid are traveling back to India and may return to the USA after some months.

Do my wife and kid go to Visa stamping again as I changed my employer?

My current visa is valid till sep 2018.So are my wife and kid visa status.

I got H1 approval in November 2015 and got stamping in January 2016.

I heard that there is no need of stamping again(for my wife and kid) as my visa is not expired yet.

Is this True?

Will they be eligible for drop box facility if they need a visa stamping.

There is no need for stamping - the visa class for dependents has not changed.