Our daughter was trached at age 6, so she ate before then. She got her trach and became vented 24/7 after her 6th birthday. And honestly, it took her all of 1 day to get back to it when they let her. They were going to do the swallow study, with the x-ray and everything. But the ST's at the hospital said it wasn't needed based on what they could see her doing. Since she has so many x-rays in her life, we tried to avoid any extra ones.
She's never had a problem eating or talking over the vent. In fact, even with an inflated cuff on the trach, she can talk. It always amazes the doctors/nurses. Now, she's not trached cuz of an actual airway issue. Hers is a neurological condition that causes her to stop breathing.
So yes, kids can eat on the vent.