I.e., would a kid in the 18th century who's playing with a stick and pretending it's a musket pretend to pull the hammer to full-cock, pour the powder in the barrel, shove the ball down the barrel with the ramrod, etc.
Children's culture in history can be difficult to study. Adult observers tend to reflect more formal types of play and practice; memoirs reflect the haze of memory and desired memory; it's sometimes difficult to tell whether schoolbook exercises represent an individual experience or a standard trope. In this case, fortunately, a look at the broader culture of children's wargaming in early modern Europe can help answer the question.
Children's play often imitates the adult world for two reasons: first, children mirror what they see; second, adults encourage it to help prepare children for the future. The encouragement of martial play among boys (only boys) in the late Middle Ages and early modern era is a good illustration of these. We have stories from hagiography of the future saint who stepped aside from the mock swordfighting to play at being a priest dispensing the Eucharist, and proverbs observing that when children play at swords, war is in the air. From the adult encouragement angle, with the rise of a visible toymaking industry from the fourteenth century, hobby-horses and swords were among the most popular items.
Although toy guns start to appear from the later half of the sixteenth century, it's really in the seventeenth that guns displace the swords of knighthood as boys' wargame toy of choice. This is in conjunction with the encouraged realism of militaristic play. Memoirs of noblemen raised at a royal court, like Louis Henri with Louis XIV, stress the popularity of fully organized "armies" of boys marching and drilling under their "commander," the king. And this was in no way limited to the elite of the elite. Army-style drills were not just a major component of the all-around education of boys at grammar and secondary school--school sponsorship of these types of exercise actually served as a marketing appeal. The Lincoln Grammar School stressed the realism of its schoolyard play in opposition to "childish games": its students "exercised in all their military postures, and in assaults and defenses." And from the 17th century, assaults and defenses meant guns.
With princes and high nobles, it seems that the guns and cannons would be smaller, boy-sized versions, but real. Louis Henri describes learning how to shoot with a harquebus that then-Prince Louis gave him, and mentions how he and the other boys (which is to say, their fathers) lavished the future king with many and diverse shooting weapons.
But moving down the social ladder to the urban middle classes (presumably), actual toy guns were exceedingly popular among boys. Actual records are scanty, of course, but archaeological digs and trawls of the Thames (where worn out or unneeded toys might be disposed of, or make their way there through a sewer or settlement) turn up toy guns and cannons as among the most numerous survivals. And for the most part, these toys appear to have been designed for mock shooting, including packing with powder and pellets to fire.
But children playing with toy guns in the manner they were designed to be used by adults is not yet the same as children making the leap themselves. For that, we turn to disciplinary and legal records of situations where boys improvised. One student of the Bodwin School participated in wargaming exercises not just by carrying a dummy gun. He actually got a candle, hollowed it out, and packed it with powder. This isn't a mock stick, but it's pretty close.
There are plenty of tragic events where children did not realize a gun was loaded, went to play with it, and killed a playmate or bystander by accident. But one case from turn of the 18th century London demonstrates the realism that permeates surviving accounts of boys' wargaming. A twelve-year-old apprentice came across his master's gun and wanted to play with it. But he wasn't content to point and cock and click, like plenty of boys did in the cases where the gun proved to be loaded. No, for this boy, playing with guns started with inserting the stick and packing it with powder.
Some caution is of course warranted. These aren't cases of boys pointing sticks at each other and making exploding noises with their mouths. And surviving sources, as I've discussed, are going to be biased towards more realistic types of games. Nevertheless, the combination of being so steeped in militaristic "play" and the general tendency to learn adulting by observation led our two improvisers to want "toy guns" that mirrored the real thing at every step except the very last. It seems likely, therefore, that just like we can all remember a range of ways we "played pretend" with "guns" when we were little, 17th and 18th century boys also scaled up towards imitating the real thing with whatever they had.
Further Reading: