Sir Elton John and David Furnish are teaching their sons about the ''diversity of families''.

The couple raise Zachary, three, and Elijah, 16 months, together and their oldest son is now beginning to understand that households often have different parents so they are keen for them to celebrate the differences in family units.

David told People: ''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.

''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 realise that there are all different kinds of families and all families are great.''

At the weekend, the couple - who entered into a civil partnership in 2005 - announced their intention to wed after same-sex marriage was made legal in the UK, and though they are planning an intimate ceremony in May, they would have tied the knot sooner if it weren't for the 'Rocket Man' singer's commitment to his Las Vegas residency.

David said: ''Elton's on this side of the world for his [Las Vegas residency show], and we're not in the UK. Had we been in the UK., we would have done it this weekend, absolutely.

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

Elton added in an interview with Matt Lauer on 'Today': ''We'll do it very quietly. But we will do it and it will be a joyous occasion and we will have our children.''