Elton John and David Furnish Teach Their Sons 'All Families Are Great'

By Mark Gray

03/31/2014 at 08:45 AM EDT

Elton John and David Furnish

George Pimentel/WireImage

Happy families come in many forms, and Sir Elton John and partner David Furnish are making sure that's a lesson their two young sons learn early.

"Our oldest is just starting to get his head around daddy and a papa, and not a mommy and a daddy, because he just started to go to pre-nursery school with other kids," Furnish, 51, told PEOPLE Saturday in Las Vegas, where John is performing at Caesars Palace.

"He's learning about the mixture of different families. We read books to him that really celebrate the diversity of families in society today. We want to make sure that our boys realize that there are all different kinds of families and all families are great."

John and Furnish are parents to sons Zachary, 3, and Elijah, 16 months, and while they know the boys are too young to fully appreciate the significance of their upcoming wedding, they're aware of the message their high-profile nuptials will send to the world.

"Call it flag bearing," Furnish explained while John took part in a photo shoot at Fizz Las Vegas. "We're living in pivotal times. I think if you have an opportunity to live by example and make people aware of positive changes in our society, I think it's a great thing."

The two announced their intention to wed Friday – one day before same-sex weddings became legal in the U.K. – while celebrating John's 67th birthday in Vegas.

Furnish adds that if they were living in England now they would have been among the first to walk down the aisle.

"Elton's on this side of the world for his [Las Vegas residency show], and we're not in the U.K. Had we been in the U.K., we would have done it this weekend, absolutely," he says.

The couple now plans to wed in May, and say they are foregoing a lavish affair like the $2 million reception they threw to celebrate their civil partnership in 2005.

"We'll go to the registry again and we'll take the boys with us," Furnish says. "Take along the one or two witnesses that we need and make it very small and intimate."

Adds John, speaking to Matt Lauer in an interview that aired Monday on the Today show: "We'll do it very quietly. But we will do it and it will be a joyous occasion and we will have our children."