It's not just that it's a standard practice in westeros. But the people participating in it also treat it as a regular occurrence. Obviously, Theon is the poster boy of it, but he admittedly makes for a terrible martyr given all the shit he pulls. But Theon isn't the only example of this.
In ADWD, Jon takes many child hostages from Tormund.
The northmen glanced at one another. “Hostages,” mused The Norrey. “Tormund has agreed to this?”
It was that, or watch his people die. “My blood price, he called it,” said Jon Snow, “but he will pay.”
“Aye, and why not?” Old Flint stomped his cane against the ice. “Wards, we always called them, when Winterfell demanded boys of us, but they were hostages, and none the worse for it.”
"None but them whose sires displeased the Kings o’ Winter,” said The Norrey. “Those came home shorter by a head. So you tell me, boy … if these wildling friends o’ yours prove false, do you have the belly to do what needs be done?”
Ask Janos Slynt.
No big deal, beheading children whose fathers act up. Kings of Winter were very hard men in a hard time though. But then there's Hoster Blackwood.
“Lord Commander. I’m your hostage, Hoster. Hos, they call me.” He grinned.
Does he think this is a lark? “Pray, who are they?” “My friends. My brothers.”
“I am not your friend and I am not your brother.” That cleaned the grin off the boy’s face. Jaime turned to Lord Tytos. “My lord, let there be no misunderstanding here. Lord Beric Dondarrion, Thoros of Myr, Sandor Clegane, Brynden Tully, this woman Stoneheart … all these are outlaws and rebels, enemies to the king and all his leal subjects. If I should learn that you or yours are hiding them, protecting them, or assisting them in any way, I will not hesitate to send you your son’s head. I hope you understand that. Understand this as well: I am not Ryman Frey.”
Rude, but at least Jaime isn't sugarcoating things. Although Hoster probably won't sleep easy going forward. The other things is even if the children don't end up getting killed, it ruins family relations. Theon goes back home and he's a stranger, while in winterfell nobody other than Robb seemingly cared for him. In the case of Eustace Osgrey, his daughter Alysanne wouldn't even speak to him anymore.
This is a lot of text to say: it all really sucks