If a 1911 that is magazine loaded but not chamber loaded is not a danger, then why don't we point them at each other when they are unloaded, or look down their barrels, etc.? Because the first rule of gun ownership is that guns are always loaded.
"Here Sally, play with my unloaded 1911." Lulz.
+1 on this. While the child may not be able to physically harm themselves with it, I want to be there when they handle and familiarize themselves with the firearm. Unsupervised "play" with a real gun could (not will, but may) lead to poor outcomes in the future when the kid is big enough to harm him- or herself.
18 months is too young for a child to be cognitively developed enough to engage in firearm safety (or drive a motorcycle, or use a band saw, or stick weld, or pan fry bacon, or engage in a variety of other tasks). Once he or she is old enough be taught gun safety, then we can begin "gun proofing the child," as it were. But until then, it's on us, the parents.