The 22-year-old Olympic diver and the 42-year-old director - who got engaged in 2015 and are hoping to tie the knot next year - are planning to have children after Tom retires.
He told The Sun: ''It's not a question of 'if', just 'when'. I've always said I'll keep diving as long as my body lets me, but the beauty of being an athlete is you retire young and you've got your whole life ahead of you.
''Once I've finished with diving there are going to be other avenues I'd like to explore. Family has always been a massive thing to us. It's what we want.''
However, Tom revealed that their first big post-Olympic project will be their wedding.
He explained: ''It's going to be next year. We haven't planned a thing yet.
''It's our post-Olympics project, something to look forward to.
''We haven't decided on a location but it will be as far away from a diving pool as possible.''
Tom also insisted that criticism of the age gap between him and Dustin is ridiculous as he feels more like the adult in the relationship.
He said: ''It's the other way round in reality - I'm the adult. I do all the cooking, organising and pay the bills. That's my end of the deal.''
Meanwhile, Tom opened up about the Oscars controversy between Dustin and Sam Smith, insisting that the singer is a ''good mate'' of them both.
After Sam mistakenly claimed in his acceptance speech for Best Original Song that he was the first openly gay man to win an Academy Award, Dustin - who won the best original screenplay prize in 2009 for 'Milk' - sent him a furious message on Twitter.
He wrote: ''Hey @SamSmithWorld, if you have no idea who I am, it may be time to stop texting my fiancé. (sic)''
However, Tom said: ''It was quite funny as we're all really good mates. When somebody has written a sarcastic tweet you can't read the tone.''
Celine Dion barely cracks a smile and yet she's the greatest guest yet.