Rachel Zoe says parents need to put their foot down when it comes to their kids riding electronic bikes ... 'cause her son was hospitalized after a bad crash.

The fashion designer took to Instagram this weekend to share her son's plight ... telling fans her 13-year-old son Skyler ended up with a "badly lacerated kidney, a ton of pain and a shattered mom" after an e-bike accident.

Rachel adds that her kiddo is in pain when he laughs or sneezes ... and, she says there's no way she's ever letting him anywhere near an e-bike again.

Zoe says any parent considering buying their kid an e-bike better think twice about it ... 'cause they spent hours in the ER after the crash. Worth noting, Zoe makes a point to say she didn't buy him the bike -- but, somehow he ended up on one.

Unclear exactly how Skyler crashed ... but, he's not the first celebrity kiddo to end up in the hospital because of an e-bike accident.

Remember, Pax Jolie-Pitt slammed into the back of a car while on an e-bike over the summer, law enforcement sources told us ... and, he reportedly ended up in the intensive care unit.

The crash was so bad, eyewitnesses said they thought Pax died. Thankfully, he was released from the hospital a few days later. He ended up crashing into ANOTHER car while on an e-bike in January -- but, he apparently did more damage to that car than it did to him.

Sounds like all's well that ends well ... though Zoe's kids are probably going to stick to manual pedal bikes from now on.