Both apples and crab apples belong to the same plant genus, Malus. Genetically, they differ only in flower color and fruit size. Crab apple trees sometimes fail to produce fruits or their mature fruits grow no larger than 2 inches in diameter. The crab apple tree itself is not toxic to humans, even little children, if gnawed on or swallowed. The only concern with crab apples are the fruit seeds, also called pips, which contain trace amounts of amygdalin. Eating a huge amount of crab apple seeds can cause problems.
Overall Plant Threat
Planting a crab apple tree in the yard doesn't pose a health or safety concern if children live in the household. Leaves, bark, twigs, flowers and the small fruits pose no risk to humans if eaten. These plant parts may taste differently -- some tart, sour or sweet -- but they are not toxic. The only concern arises if children pick and eat lots of fruits in late summer and fall. While the fruit flesh is edible, the seeds contain a sugar and cyanide compound called amygdalin.
Crab Apple Seeds
Crab apple fruits simply are miniaturized versions of apples. To a child, the larger amount of apple flesh makes it easier to avoid the pithy core and seeds when eating an apple. Crab apple fruits make mouth-size bites for chewing. However, most crab apple fruits don't develop as sweet a flavor as modern apple fruit varieties. The child may quickly spit out a crab apple, finding it too tart. The amygdalin in the seeds degrades into tiny amounts of hydrogen cyanide once exposed to stomach acid.
Do not confuse the toxin arsenic with amygdalin. Only amygdalin exists in crab apple seeds -- and at no more than 10 percent of a seed's chemical content, according to Purdue University. Moreover, the thick seed coat on crab apple seeds is tough enough to withstand stomach acid. The potential trouble arises when the crab apple seeds are chewed up and the seed coat crushed, exposing the amygdalin. The human body expels trace amounts of cyanide in the amygdalin. According to Purdue and North Carolina State universities, large quantities of crab apple seeds -- more than one-fourth of a cup -- would need to be consumed to truly pose severe health risks.
Effects of Cyanide
If a child eats a couple of crab apple seeds, scold him and tell him not to eat the bad-tasting crab apples or seeds. You can monitor his metabolism and demeanor if it soothes your anxiety. You can also contact the local poison control center for advice and direction. You would only need to be concerned about significant amounts of cyanide in the body if your child showed rapid breathing, elevated heart rate, restlessness, dizziness, weakness, headache, nausea and vomiting, according to the Centers for Disease Control and Prevention website. Extreme poisoning from cyanide causes a temporary coma and death.