Kids love bubbles. Even big kids love bubbles! One singing motivator activity my primary loves is the Bubble Blower. It's really simple, too. Adults or kids can help with this one.
Get some bubbles, the battery operated bubble blowers are best. Make sure your batteries are fresh and you have a good supply of bubble solution. Choose a helper. The better the primary children sing, the more bubbles the helper blows. Choose a new helper for the next round.
Option: Have two bubble blowers and do one for each side of the primary room.