Prime Minister Malcolm Turnbull's truck-loving grandson Jack steals the show again

If Malcolm Turnbull is wondering what his grandson wants to be when he grows up, he may have given him a little inspiration.

Almost as soon as the prime minister-grandpa rolled into a truck rally in Sydney today, Jack Turnbull Brown stole the show.

"I want go in the trucks!" the two-and-a-half-year old squeaked as he rushed into Mr Turnbull's arms.

The dozens of trucking business owners, the employment and infrastructure ministers and other Liberal MPs who'd been waiting hours for the prime minister to arrive didn't seem to mind the extra wait.

"You want to see some of the trucks Jack? Ok, yeah," Mr Turnbull laughed as the assembly of hangers-on followed him to a nearby hauler.

Mr Turnbull sat his grandson on the driver's seat and encouraged him to blow the truck horn.

"Give it a little twirl," he enthused.

The pint-sized Jack tried - but it didn't work.

"He's very happy in the driver's chair," Mr Turnbull reckoned, shortly before doing the job himself for the cameras.

Earlier, Jack jumped up and down for the sea of lenses following his cheeky movements - including playfully trying to evade his mother's arms as she ran after him.

Jack made a cameo appearance earlier in the campaign, interrupting his more famous grandfather's press conference in May.

If cuteness is any measure, Mr Turnbull has certainly got a secret weapon.