I didn't understand your reference to 'packaging' to be loaded cartridges. I assumed you were comparing apples to apples: loose black powder in a metal or plastic can vs loose smokeless powder in a plastic can. Certainly a loaded cartridge does an excellent job of containing the powder, better than a metal or plastic can with a screw on lid.
With regard to loose powder, the 'authorities' have enacted regulations that treat real black powder, synthetic black powders and smokeless powders in loose form differently. It was this difference that I assumed you were referring to as making black powder more dangerous.
With regard to loose powder only:
Black powder is classified as an explosive by BATFE, vs the substitute black powders and smokeless powders which are classified as a propellant. I understand this to be because of black powder's significantly lower ignition temperature. You grouped black powder and synthetic black powders together with regard to fire department storage requirements; in all the jurisdictions that I am aware of the storage regulations for real black powder are different, allowing the synthetic powders, and smokeless powders, to be stored in the open on store shelves while real black powders must be kept in a purposely designed magazine when in large amounts.
There is reasonable debate as to whether loose black powder is indeed more 'dangerous' than loose synthetic black or smokeless powders, the BATFE classifications notwithstanding. Goex had begun a letter writing campaign to the Treasury Department to get real black powder reclassified, citing a significant body of work attempting to show it posed no more a problem than the other powders in a real world situation (it's a bit silly to be concerned about the difference in ignition temperatures when structure fires are universally hotter than either ignition temperature by several factors). I'm unsure of the status of that effort now that Hodgdon has purchased Goex.
With regard to your scenario of a child spilling loose powder: I won't rant about the issue of storing powder (or household chemicals for that matter) in a manner that would allow that to happen. However, be aware that if the child spilled the powder and then lit a match to it, it would flash and burn quickly, probably causing 2nd (or rarely even 3rd) degree burns, but it would NOT explode. As to how to clean up loose powder: if it's on a hard surface, sweep up as much as possible with a straw broom, then wash the area down with soap and water and then squeegee the water up to remove the dust. If it's on a carpet, thoroughly wet the carpet and use a wet/dry vacumn to suck up the water. Then deal with the wet carpet in whatever manner appeals most.