Its not cause its a choking hazard, just that the grains dont start to get digested till they are older. If they eat an awful lot of bread you could see the problem there with them passing properly is suppose.

DD1 just plain doesnt like it since she got molers (full set chompers at 12mths) cause the seeds get stuck in her teeth and she gets agro at it. So she has wholemeal, took a little while for her to agree to eat it though.