The narrator of this piece actually doesn't suggest that the Irish eat their own children; he suggests that the Irish sell their children to the English as a source of income. Not only would it provide the Irish with much needed money, but it would also mean that their families have fewer mouths to feed and backs to clothe, and so amount to a savings for them as well. However, as you point out, Jonathan Swift, the author, does not actually want the Irish to take this action. He is suggesting it satirically, as a way of pointing out the deplorable way the English landowners treat the Irish. If the English are willing to figuratively "devour" Ireland, buying up all the land and hiking rents so high that families can afford nothing else, then -- he pushes to the ridiculous conclusion -- why wouldn't they be willing to literally devour the Irish too?
Swift seems to want the Irish to take better care of themselves so that their country does not remain in the terrible state in which it exists at that point. Since the narrator thinks selling babies for food is a great idea, we can reasonably assume that the ideas he thinks are terrible are actually good. He lists a number of "other expedients" toward the end of the piece, and he says, "let no man talk to me of [them]." He lists, among others, raising taxes on absentees, using only products made in Ireland, "rejecting the materials and instruments that promote foreign luxury," curing the faults of Irish women, exercising temperance in all ways, ceasing the fights among Irish factions, teaching landlords to be merciful, and so on. These are the measures Swift actually would prefer the Irish take: after all, the Irish were somewhat complacent when the English moved in and started buying up all the land, taking over the government, and so forth. Now, he wants them to behave better -- more ethically, more responsibly -- and so, perhaps, resume control over their own economy and way of life.