The first step is to reduce the number of instruments. In many kirtans, devotees spontaneously pick up instruments no matter how many are already in session. But Dvija Vara advises that just one pair of kartals and one mridanga (no whompers or gongs) are usually enough even in a large kirtan.
I know that the parents want to encourage the boys to learn the mṛdaṅga and one of the best ways to do that is in a live kīrtana. There’s nothing like struggling to keep up with the big boys whilst enduring their discouraging frowns. That’s how I learnt to play instruments under the loving scowl of say, Kūrma Prabhu and Govinda Svāmī’s sternness. But, as is mentioned above, there really is no need for more than one mṛdaṅga and one set of karatālas in the temple room. Maybe two karatālas.
The article referred to above has a few sensible recommendations.
I’ve ordered the sound meter for our temple room.