Roof moss removal

The bleach mix will be dilute enough that it will not be of harm. I've used it myself at least a few times to kill off algae that has accumulated.

You can also use things like Oxy-Boost and Stain Solver, a bleach substitute which I believe contains some hydrogen peroxide. It will also work against light moss and algae, yet perhaps be less harmful to plant life underneath.

More importantly is to fix the source of the moss. Roofs that gather moss tend to be too shaded, under big trees that stop it from drying out. You may need to open things up, just by a bit, but enough to let it dry out. Yes, those trees are a natural source of air conditioning, but trees tend to grow. So trim off branches that overhang the roof. Cut a few others out to let the sun in.

For roofs that have only a bit of green, you may find it is sufficient to add zinc strips along the top. The zinc leaches out, keeping the roof clean of moss accumulation. There are also shingles with a moss inhibiting additive that prevents moss from growing. Copper strips should also work, and copper flashing is easily available. I've even read that you can glue (use silicone) copper pennies just under the edge of the top row of shingles. They are mainly zinc anyway.

If the moss had accumulated heavily, the problem is your roof likely needs repair, as it will have been too wet for too long. The shingles will need to be stripped off and replaced, but probably the roof decking will be soft and need some repair too. This can best be judged by a professional who will inspect the roof carefully.

Should I worry about this? (does it reduce the effectiveness of the shingle). If yes, then question 2 come into play.

There's certainly more important things to worry about in life, but, yes, Moss will, over time, shorten the lifespan of asphalt shingles.

Can it be corrected in the area that are truly unsightly with a chemical or something? I have kids so it would need to be safe. If yes, question 3 comes into play.

Yes. Actually, you want to correct it over the entirety of the roof. You can purchase spray-on as well as granule based moss killer. That is what you want.

If some cleaning can be done to fix, is this a DIY or does a service have to be contacted?

You can DIY or you can hire a service. If you live in a moss-friendly region (such as the Pacific North West of the USA) then you'll find all sorts of people that do pretty much just this. Either way, be sure to hire people that use very gentle cleaning methods. You don't want power washing or anything of that sort.

Once corrected, is there any preventative measures that can be done to avoid this?

The only real remedy is to not shingle a roof with asphalt shingles in moss-prone regions. That's why you see a lot of standing seam metal roofing in wet areas. Barring that, you just need to make the moss prevention an annual chore.

Some claim that zinc strips will work (as zinc will kill the moss) though, at least around here, you can find plenty of roofs with zinc strips that also still have plenty of moss on them, so I tend to think that's a bit of a scam solution.