2010 data:
1,006,374 of 22,872,151 (4.4%
+ 0.07% MOE) married opposite sex couples had adopted OR stepchildren
117,884 of 2,267,016 (5.2%
+ 0.30% MOE) unmarried opposite sex couples had adopted OR stepchildren
vs
5,079 of 38,778 (13.1%
+ 2.83% MOE) married same sex couples had adopted OR stepchildren [reported census data]
14,967 of 55,849 (26.8%
+ 3.36% MOE) unmarried same sex couples had adopted OR stepchildren [reported census data]
or
20,060 of 94,627 (21.2
+ 2.26% MOE) same sex couples regardless of marriage status had adopted OR stepchildren [unreported data based on other sources]
So what can be concluded above is there are more adoptions/stepchildren from opposite sex couples (1,124,258) than there are from same sex (20,046 reported, 20,060 unreported). However, the % of same sex adoptions is higher than that of opposite sex, but this is a different debate entirely.