3: 2 adults and 1 child. I always prefer to do it if possible, especially if I book a rate with breakfast. In most cases there's no extra upon booking whether you select 2 or 3 people (assuming the use of existing bed), but I wouldn't want the third person to be charged extra on arrival if I didn't select it upon booking. For IC Bali all the room can be booked for 3 people so there's no penalty (if you want to select 4, though, you're limited to duplex or vila; depending on how old the children are I'd contact the hotel to enquire).
Note that when I upgraded to the duplex room, they suggested we still add an extra bed because they said the sofa bed wasn't comfortable enough. The cost was 24 USD ++ per child / 48 USD ++ per adult which I thought was OK. It looks like they forgot about it as when we arrived they had set up the sofa bed instead (since the booking was for 3), which was perfectly fine.