Hilary Duff's son changes every week.

The 26-year-old actress is enjoying watching two-year-old Luca, with whom she has with her estranged husband MIKE COMRIE, reach new milestones and she's shocked by how fast he's growing up.

Speaking to E! News, she said: ''There's no word good enough to describe how he's changed my life and how amazing he is. He's so much fun and it's amazing to watch him grow. Week by week he changes so much.''

Meanwhile, Hilary and Mike, who announced their separation in January, are keen to co-parent the youngster ''peacefully'' because his needs are the most important thing to them.

Hilary said previously: ''We're really good friends and spend a lot of time together. We're just trying to figure out what makes us happy, but we have Luca as our priority. We're going to do it in the most peaceful way.''

However, the blonde beauty admits the toddler is definitely keeping them on their toes as they can't take their eyes off him for one second without him getting into mischief.

She explained: ''Luca's two, so he has a strong personality. He's spirited. That's a good word for him.

''He's talking a lot and trying to put words together, which is a big deal. But sometimes he does test me. I have a toddler bed on order, but he's already jumping out of his crib! I hear a thud and I'm like, OK, he tossed himself out. He's so funny. I say, 'What are you doing?' And he's trying not to smile because he knows it's kind of naughty. He opened his own door recently - I couldn't believe it.''