The 37-year-old singer, who re-joined the group last year, still doesn't have any kids of his own with wife Ayda Field, and has been making to most of getting to know band-mates Gary Barlow and Mark Owen's youngsters.
Dad-of-three Gary Barlow, 40, told the Daily Star, 'My son Daniel loves Rob because he gives him footballs and he even gave him a pair of David Beckham's old boots.
'He thinks the best thing that's ever happened to me is knowing Rob.'
Mark Owen added, 'My children Elwood and Willow love Rob.
'My son draws pictures for him and Ayda. He's obsessed with him.'
Meanwhile Robbie revealed that he has hopes of starting his own family soon.
'Ayda thinks I will be a good dad,' he said. 'I have no idea how many kids we will have – only time will tell.'