Children walked up to the Bananas - towering above six feet - and gave them a hug at the Royal Australian Mint, which has marked the anniversary with two commemorative coins.

The mint will splash 30,000 collectible 20 cent and five cent pieces with the yellow, blue and white figures of B1 and B2.

Ahead of the event, mint chief executive Ross MacDiarmid admitted he didn't know whether crowds would make heads or tails of it.

"You're always concerned about how these things are going to go, whether they will be as popular as expected," he said.

But the appearance of the Bananas drew crowds of families who lined up to meet the mischievous duo and see the new coins, which won't be widely circulated.

The Rat in a Hat replaces the more stately, less scheming echidna on the commemorative five cent piece, the first to be printed with colours in Australia.

On the 20 cent piece, the Bananas chase teddy bears Morgan, Lulu and Amy as they have done since becoming an afternoon TV staple for kids in 1992.

After commemorative coins marking 50 years of Play School proved a hit, the mint decided Bananas in Pyjamas deserved a party too.

"I think anything that celebrates the interaction of children and characters that come out of Australia is worth commemorating," Mr MacDiarmid said.

Their popularity on Sunday shouldn't have caught him unawares.

Children wanted to see their beloved television characters live and the coins were a way to connect them, he said.

Bonner's Stuart Gray waited in line with his children Calum, 10, Caitlyn, 8, and Hunter, 4, who have grown up watching the show.

"We knew the kids would like to see it, certainly the younger ones," he said.

The coins are available for purchase at the mint's eShop online.