Cockpit visits are still allowed on the ground, it's only in flight that it's no longer possible.
Well that's good, at least.
I still remember when I was fortunate enough to failover to a concorde when our 747 was grounded ~20 years ago and got to visit the cockpit in flight. There was a seam between two portions of the cockpit (a little less than an inch wide) that only existed when the plane was supersonic, and it closed tight when not.
Wouldn't have been able to scare a kid into thinking they could get their hand stuck in there if the plane was still on the ground ;)
Of course whether or not in-flight cockpit visits were still allowed, that particular experience wouldn't happen anymore.
Ah well, it seems that those days will never return.