- Grapes are round and larger than a child's airway and may lead to occlusion.
- Food with a smooth, deformable surface can form a tight seal.
- Grapes are "the third most common cause of food-related fatal choking episodes".
- Children below 5 years of age don't chew as good yet.
- Grapes should be cut up for children.
This is mostly about grapes, not blueberries, but blueberries are probably similar. According to wikipedia, they are "5–16 millimeters (0.20–0.63 in) in diameter".
I mainly quote (1), since I don't have full access to (2) and (3), so their relevant conclusions are also taken from (1).
The physical features of a foreign body are important in determining the potential effects of aspiration. Compared with grapes, small, hard objects or foods may more easily be dislodged from the rest of the upper airway with chest or abdominal thrusts. They are also more likely to pass through the larynx and come to rest in the right main bronchus, causing respiratory difficulty but allowing ventilation of the left lung. In contrast, round foods or objects that are larger than a child's airway may cause occlusion at the level of the laryngeal inlet, resulting in complete airway obstruction that is rapidly fatal if not alleviated promptly. The threat is bigger still if such an object has a smooth, easily deformable surface allowing it to form a tight seal, wedge, and thus becomes very difficult to dislodge with first aid manoeuvres.
(from (1) citing (2))
Grapes are a popular food with young children but are ideally suited to cause obstruction of a paediatric airway and are the third most common cause of food-related fatal choking episodes after hotdogs and sweets.
(from (1) citing (3))
One of the authors of (1) was also interviewed in (4):
“It is not just tiny, little kids – we would suggest up to the age of five the kids are more at risk because they don’t chew as well, their swallowing is not quite as coordinated and they get distracted when they are eating,” said Cooper.
In (4), also Tina Newton, "a consultant in the emergency department at Birmingham Children’s Hospital", was interviewed
Like Cooper, Newton recommends that the fruit should be cut up for children, adding that parents should also be aware of what to do if their child chokes. “For a child, turn them upside down and slap them hard on the back between the shoulder blades,” she says.
(1) Lumsden AJ, Cooper JG. The choking hazard of grapes: a plea for awareness Archives of Disease in Childhood 2017;102:473-474. Link
(2) Reilly JS, Walter MA, Beste D, et al. Size/shape analysis of aerodigestive foreign bodies in children: a multi-institutional study. Am J Otolaryngol 1995;16:190–3. https://doi.org/10.1016/0196-0709(95)90101-9
(3) Altkorn R, Chen X, Milkovich S, et al. Fatal and non-fatal food injuries among children (aged 0–14 years). Int J Pediatr Otorhinolaryngol 2008;72:1041–6. https://doi.org/10.1016/j.ijporl.2008.03.010
(4) Nicola Davis: "Lack of awareness of grape choking hazard puts children at risk, say doctors", The Guardian, 2016.12.20. Link