Galaxy Patrol

Jake is a sci-fi buff, so when he's abducted by aliens he's delighted.
But when he realises that his younger sister has also been taken, he's
not so pleased. What do they want with her?
They find themselves on a space ship manned by aliens from a
confederation of planets. They form part of a Galaxy Patrol team,
ceaselessly patrolling the galaxy to check on alien incursions into
less advanced worlds, such as Earth. They recruit children as local
agents to help them in their work. Children believe: adults don't. Now
Jake and Rosie's first mission is to rescue the Queen, who has been
taken over by an alien bug ...