Most commercial mosquito or bug repellents use the active ingredient known as DEET ( N-Diethyl-M-Toluamide, N-diethly-3-methylbenamide ). DEET is not just a repellent, it is actually toxic/fatal to all insects and kills them. Typical repellant concentration is 7% DEET. There have even been products as concentrated as 100% DEET, marketed as "deep woods" or "ultra strength" which you find in outdoor/sporting goods stores, often in the hunting/fishing areas.

FDA/EPA recommends no higher than 10% DEET for children. Concentrations higher than 20% only lengthen the effective time the product works, they do not provide better protection.

Given the toxic nature of DEET and the fact that it is indiscriminate about what it effects, use of DEET products on children poses certain risks (the manufacturers, of course, don't elaborate more than required by law).

Here are typical warnings from two pharmacy sites :

1.  Keep out of reach of children.

2.  Hazards to humans.

3.  Causes moderate eye irritation.

4.  Harmful if swallowed.

5.  Do not get in eyes.

6.  Use of this product may cause skin reactions in rare cases.

7.  Wash treated clothing before wearing it again.

8.  Wash hands before eating, drinking, chewing gum, using tobacco or using the toilet.

9.  Don't apply DEET products to sunburned, cracked, bruised, or irritated skin

10.  DEET may damage synthetic fabrics

Add to this people who think "more is better", combined with the following warning (same product):

Notice: Buyer assumes all responsibility for safety and use not in accordance with directions.

DEET free products  are available, especially on the web (not typically available at drugstores. Check "alternative" stores... health foods, organic foods, etc.). The alternatives generally work for a variety of insects, including mosquitoes & black flies, repelling by scent.

Look for the following natural ingredients (and yes, some of them smell, it's how they work)

1. Lemon Eucalyptus Oil

2. Citronella (can irritate skin a bit) - it works, that's why Citronella candles are marketed for backyards

3. Patchouli Oil

The CDC registers Lemon Eucalyptus Oil as an approved repellent. It is, as one might say, 'quite aromatic'.

" Oil of lemon eucalyptus [p-menthane 3,8-diol (PMD)], a plant based repellent, is also registered with EPA. In two recent scientific publications, when oil of lemon eucalyptus was tested against mosquitoes found in the US it provided protection similar to repellents with low concentrations of DEET."

One final note. very few  mosquito species carry West Nile virus. Those that do reproduce in stagnant water. Check your yard for standing water: old tires, cans/buckets, flowerpots, gutters, trash can lids, anything that can hold rain, etc. Moving bird bath water (waterfalls, fountains, etc.) do  not allow mosquito larva to grow. Change "standing water" bird baths every couple of days. There are a number of useful web sites, FDA, EPA, etc. The Mosquito Control organization has a concise "summer precautions" page at:

            http://www.mosquito.org/resources/summer-safety.aspx

Columbus & surrounding municipalities have "fogging" programs in effect, but that chemical is, again, toxic to many/all insects. You can call the city government for your area and ask to have your property exempt from fogging. In Columbus, you must call each year to stay on the list. "No fog requests are also helpful in avoiding chemical irritation to those with asthma, allergies and other respiratory health issues.

In the habitat  yard, of course, we "do not fog" so predator bugs (dragonflies, praying mantids and others) survive to control mosquitoes.