A new caravan with nearly a thousand Central American migrants trekked north on Friday.In the heat of the Mexican sun, many took their children with them as they left Tapachula, a city bordering Guatemala, and marched for the town of Mapastepec, about 60 miles away.That's where they hope to join other migrants, bound for the U.S.Patience had run out for many in the group, who say they want to leave Mexico.Local authorities had promised them paperwork, in the form of humanitarian visas, to settle in the country and work.But those haven't arrived.It's left many, like Cuban migrant Orney Perez, struggling to support themselves. "We need the documents to be able to work. Because if not, they do not give us work and we need to work to be able to support ourselves because we have to pay rent, food and how can we do it? We are immigrants."Mexico hopes the offer of visas would prevent more migrants from walking toward the U.S. border.But many are skeptical of such deals, and Mexican authorities' ability to deliver on their promises.