Hi Leaf,
It seems a bit unrealistic to expect those crossing the border to engage in illegal activities to self-identify as such, thus it will be difficult to come up with a number. I think you might be interested in data pointing to the problem of human trafficking though and that you might consider United Nations reports to have a degree of credibility.
This is older data (2010-2012) but the maps and graphs are interesting. Page 35 shows El Salvador as a source of illegal adoption and child selling.
The regional overview for the Americas begins on page 70 and I am excerpting:
"Regional overviews
71
traffickers in the Americas is also relatively high, ranging
around 40 per cent for prosecutions as well as convictions.
These shares are similar in both subregions, even if some-
what higher in South America. A closer look reveals that
Central American countries record higher shares of female
involvement in the trafficking process (which may be
related to the profile of the victims detected there),
whereas Canada in North America reported a much lower
female conviction rate.
Profile of the victims
The profiles of the victims detected across the two subre-
gions of the Americas are similar. Child trafficking
accounts for almost 30 per cent of the total number of
detected victims, with adults making up the other 70 per
cent. These shares are similar to those found for the 2007-
2010 period.
A closer look at the two subregions brings to light some
differences in terms of the profiles of detected victims.
While in North America and in the South Cone of South
America, adult trafficking accounts for a larger share of
victims than the regional average, the share of detected
child trafficking is relatively high in Central America and
in the northern part of South America.
Most of the detected child victims are girls. Out of every
three children detected as victims, two are girls and one
is a boy. This breakdown applies to the whole region. The
females also dominate among the adults. Adult women
account for approximately half of all detected victims in
the Americas, whereas some 20 per cent are men.
There is a clearly increasing detection rate of children in
North and Central America and the Caribbean. "
I hope this will help with our conversation.
May God bless you.
jt