No, there were NOT "many" school age children, if you read the article.  "...many of those inside the truck appeared to be adults in their 20s and 30s but that there were also what appears to be two school-age children, as well".  

It is NOT obvious many were Mexicans.  What is obvious is they were smuggled into the country.  Not everyone coming over the southern border are Mexican citizens.  

You think human smuggling started January 20, 2017?  IF YOU READ THE ARTICLE, it actually describes other cases that happened - in 2003, and last December.  December comes before Trump took office.  You need to read some more, and you will find that illegal human smuggling has gone on for decades, and you don't read much about the ones that deliver their cargo without killing them, but there are plenty.

Finally, there is absolutely nothing in the article that indicates these people are to be sold as slaves.  You've made up quite a tale there, including the horse meat.