I would never advise anyone to do anything illegal. In particular I would not write down any recommendations of illegal activities, no matter how morally justified the illegal activities might be, and how morally repugnant the injustices are that the illegal activity seeks to redress. So this is purely on the hypothetical plane, an ivory tower exercise, just a guy blogging about what moral people might do in a better world, rather than in our real, often immoral world of Steve Kings and Murrietas.
So here, in outline form is a moral argument for setting up an underground railroad, beyond the grasp of the local coyotes who now arrange transport for the immigrants to the United States from Central America, and for providing sanctuary for refugees from violence and poverty.
It's really a simple moral argument. It's what philosophers call a consequentialist moral argument. Here is the bare bones outline of this type of argument, as presented in Critical Thinking: The Art of Argument, by Rainbolt and Dwyer.
(1) Action A will produce happiness/unhappiness
(2) It is morally good/bad to produce happiness/unhappiness
(3) H should/should not do A.
In an oversimplified form we can apply this to the situation of the Central American children by writing:
(1) Children are living under threat of violence and in poverty in Central America
(2) It is wrong to allow children to live under threat of violence and in poverty
(3) We should "suffer the little children to come unto" us.
The issue is obviously more complex than what I presented in the outline. Can we afford to take care of refugees? This is still the wealthiest nation in the world, and we can comfortably absorb a lot more people than our current population. They aren't our children: why should we care about them? The situation in Honduras and El Salvador is partially a byproduct of both the drug consumption in the U.S., and unintended consequences of the "War on Drugs". So we do have a responsibility to do what we can to alleviate the suffering.
Further, this is a moral argument in which I make the assumption that we should care about children. You can accept my premise that it's wrong to allow children to live in terror and poverty, or not accept it, but I view it as a compelling moral argument.
So, assuming that my argument is strong and cogent, how do we assure that the children are protected? The solution of many parents in Honduras and El Salvador is to send the children to the U.S., so that's a good practical starting point. Our laws are now being interpreted in a way that denies the children sanctuary. One historical model in the U.S. for bypassing laws which declare a class of people "illegal" is that of an underground railroad. The railroad was set up to aid people fleeing oppression
So I would argue that it's morally defensible to build an underground railroad to help refugees from Central America, particularly the children. But I would never advise anyone to do it. Because that would be illegal.