DACA is not about children. The beneficiaries are older teens and adults.
The Democrats apparently believe - without any discernible strategy - that "immigration" is a winning issue for them in November. Somehow, they expect that people will vote for their candidates if they simply claim that Trump and the Republicans are MEAN! If they deal on DACA, this takes the issue away.
Simple as that.
In my opinion, Trump should just say, "No more bargaining. I'm going to enforce U.S. immigration law as it currently exists. If you don't like it, change the law." Then arrest and deport everyone who is breaking the law.
Simple as that.