Jessica Biel's sons are "besties" with one another

Speaking on The Tonight Show Starring Jimmy Fallon, she said: "I think they are, I really do and I really was worried you just never know what’s going to happen and how your older one is going to feel about the little one. Just think each other are so funny, and it’s so amazing to watch."

Meanwhile, Jessica previously confessed she feels like she has "a thousand" children.

Asked if having two kids is harder than one, the actress and mother of two said: "A very wise friend of mine said, 'One is a lot. And two is a thousand. That's exactly the way it feels. You're like, man-on-man defense, one person's here, one person's over there. It is a wild, wild ride."

But having already been through the baby stages once, Jessica thinks that has made it easier with Phineas and they are currently sleep training him more successfully than while Silas was his age.

She added: "It's so hard to let them cry for even a few minutes. That's the sleep training we were doing. Phin did a beautiful job. We never really followed through with Silas in a big way with the sleep training.

I think it was because he was a first child, we were nervous, we couldn't bear the thought. Now it's like, 'Yeah, yeah, yeah, you're going to be fine. You're going to make it. You'll be OK.'"