Arnold Schwarzennegger's 16-year old son Chris is no longer an adorable little kid ... he's a BEAST who looks very much like he could kick the crap out of you.

Chris Schwarzenegger and his mom Maria Shriver were cruising around Santa Monica over the holiday weekend... and the famous kid has clearly packed on a ton of muscle and TOWERS over his mom.

As you might recall ... Arnold's love child Joseph Baena turned 16 in October and also bears a striking resemblance to his beefed up dad.

So we gotta ask ...