My cat just had kittens I tried the same thing and he tried to attack them luckily mum was there to fend him off but my advice is to keep little ones away from a male cat as he will attempt to kill off the kittens. Hope this helps
When Should I Introduce The Kittens Father To Them?
THe mother will let him know when he can approach so let nature take its course but be careful, toms have been known to kill kittens if they are not theirs.