transracial adoptions have their issues. There are however not enough multi(ie more than two races) racial adoptions around to draw any conclusions. You could ask a couple of Mumsnetters who have children adopted from more than one country what they think though for a opinion.
Social workers prefer to place within ethnic groups - of course they do. It is by far best solution if possible but its rarely possible.
Once a child has been relinquished for adoption there is no ideal option anymore - at that point it becomes the next best option and there is a kind of hierarchy of desire includig but not exclusively race.
I'm not an ideal parent - I'm single, I'm a differnt race to my DS, I work, I listen to the Archers. I am still many million times better than the option of growing up in the institution he was in and beleive me - people weren't queueing around the block to adopt him - three months premmie, extermely delays teh size of a six month old at 1yr, suspected cerebral palsy. Many of the chidlrne show these kinds of challenges becasue of the conditions they live in. Even the best institutions (and DS's was very good) aren't good
I don't know how old your DC's are but imagine a 5 year old who lives in a dormitory room with beds about one foot apart. Everything is communal - no clothes or shoes of their own that fit - just whatever comes off the pile first, no favorite toys, no favorite food, same meals every day with slight seasonal variations, no days out no books, no bedtime stories, don't bother crying becuase it doesn't have much affect.
Fast forward to 15 - life is most likely on the streets in crime or prostitution or ended early by suicide or illness. And to be honest no-one much will care anyway unless you keep in touch with your fellow inmates children becasue no-one "owns" you, you don;t belong anywhere or with anyone.
Dealing with multiracial issues is a price I'm afraid my son will have to pay for the chance of a better life than that.