Be aware that if you expect your blue muffin to fruit you will need a second variety of V. dentatum to serve as a pollinator and it also has to bloom at the same time as your blue muffin.

My own blue muffins are not dense enough to deter children but they are only three years in so ymmv.

put in a fence.. its children ...

the inherent problem.. is trying to grow a vigorous hedge.. in shade.. under large trees ...

those kids might be in their teens.. before the hedge actually accomplishes what you want and stops kids ...

ken

PS: temp fencing need not be permanent.. nor outrageously expensive ....

As a former child, I can tell you that if your goal is to stop children, there isn't a viburnum in the world that will work. If you could grow a thick, nasty rose in the shade, or something else with wicked thorns, that might work. However, it does sound like a more practical alternative would be a fence.

I also strongly suspect that your idea of a 'very tall hemlock' is much shorter than my idea of a 'very tall hemlock'. You aren't growing anything under my idea of a very tall hemlock because there isn't any light or water for at least 15 ft from the trunk in all directions.

I had issues with Viburnum beetle on my Blue Muffin, and after several years of poor flowering and swiss cheesy looking leaves, it got shovel pruned and burned in the fall when the beetle eggs were in the twigs. I wouldn't advise planting them at all in this area.

Swamp azalea are lovely plants, and will grow fine in ordinary to wet conditions. They need quite a bit of sun (at least half day) to bloom well, but when they bloom the scent is absolutely wonderful, rather vanilla-like.