The Israelites departed the Sinai Desert, where they had been encamped since the giving of the Torah, and start journeying towards the Promised Land. And the problems begin almost immediately. First they complain about the length of the "arduous" journey (three days!), and then, for lack of anything substantive to grumble about, they gripe about the miraculous and extremely tasty Manna. This form of testing G‑d wasn't new; it had actually become fairly standard behavior. Altogether, the Jews tested G‑d ten times before He disgustedly declared the entire generation unworthy of entering the Holy Land.
Ironically, the Jews seemed to be following G‑d's example. The Mishna (Ethics 5:3) says that "with ten tests our father Abraham was tested [by G‑d] and he withstood them all—in order to make known how great was our father Abraham's love [for G‑d]." This raises the question: isn't this a tad hypocritical on G‑d's part? If it is acceptable for G‑d to test Abraham, why was it not appropriate for the Jews to reciprocate in kind? If He can dish it out, shouldn't He be able to take it as well?!
This is a powerful lesson for us all. When faced with difficulty and challenges we must keep in mind that this is actually a display of trust on G‑d's part. We must live up to G‑d's high expectations, and then the test will have outlived its purpose and will vanish.
I think that a nisayon without an obvious purpose leaves a person feeling lost. I and several friends have sons engaged or dating non Jewish women. We have davened. We have read Tehillim. We have given tzeddakah. We have asked for prayers at Kever Rochel, the Kotel and Maarat Hamachpelah. No change for any of us. We have lost hope.
I'm so sorry to hear of your pain. Each of your prayers and mitzvot are precious to G-d, and none are in vain. May G-d bless your families in abundance, and may you merit true nachat (joy) from your children.