If he actually does have one, he's obviously not trying to keep it too secret given that he keeps doing tweet-and-deletes (which draw way more attention than a normal tweet, btw) about said "son" to his 5 million followers.
If he doesn't have one (which we strongly suspect is the case) it's a really, REALLY stupid joke - and one that got old a few tweets ago.
Apparently, Rob doesn't care what we think, though, because he's at it again. After causing yet another frenzy with his "my son" 4th of July tweet, Rob has taken to the social media site with yet another tweet about his probably made-up child.
"I'm about to go pick up my Son from the port and can't wait to watch a great movie with him, Suggestions anyone ? He's 6," he tweeted (and deleted) the other day.
After the message disappeared, Rob didn't say anything about getting hacked, like he has in the past when something strange pops up on his account.
So, again, we're left with our two possible scenarios: Rob has a secret son and this is his way of breaking the news OR Rob doesn't have a son and doesn't realize that his little joke is getting really old.