There are Muslims visiting graves (Shrines) seeking divine help. They think that the people in the graves act as mediators between them and Allah Taala. They alsothink that the people in the graves will make recommendations to Allah Taala. Surprisingly, some times it appears to be true. I came across two families. They didn'thave children for seven years after their marriage, but when they visited the shrine, in the next year they got a baby. So, they think that it's because of the recommendation of the man in the grave. I try to convince them that the help is purely from Allah Taala, butI can't explain why they didn't have kids for seven years, got one in a year after visiting the shrine. Please help me in explaing them.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
We ask Allah to pour on you, us and on all Muslims His blessings and guide us to the words and acts which please Him. We ask Allah to make the truth clear to us and help us follow it. We invoke Allah, The One to open our hearts to the truth and accept it and show us the untruth as it is and protect us from following it. O Allah! Place us on the right path and among the callers to it and do not make us devious and astray.
Dear brother,
You should exhort these people whom you mentioned in your question. Call them to the truth with wisdom as Allah Says (interpretation of meaning): {Invite (mankind, O Muhammad SAW) to the Way of your Lord (i.e. Islam) with wisdom (i.e. with the Divine Revelation and the Qur'an) and fair preaching, and argue with them in a way that is better. Truly, your Lord knows best who has gone astray from His Path, and He is the Best Aware of those who are guided.} [16: 125]. Allah by His Kindness, Mercy and Generosity made it possible for His Creatures to contact Him directly without mediators. Whoever wants to make repentance no one can stop him from doing so. Only he needs a genuine decision to make repentance by his intention, words and acts.
Whoever wants to worship Allah, should worship Allah as He legislated without any mediator. Anyone who is in need has only to raise his both hands towards Allah and ask for what he needs, trusting only in Him, imploring Allah with His Good names and His Great Attributes as well as one's own righteous deeds.
Allah surely will accept his supplications provided he does not ask something forbidden or break human relations. Allah Says (interpretation of meaning): in this concern {And when My slaves ask you (O Muhammad SAW) concerning Me, then (answer them), I am indeed near (to them by My Knowledge). I respond to the invocations of the supplicant when he calls on Me (without any mediator or intercessor). So let them obey Me and believe in Me, so that they may be led aright. } [2: 186]. Allah also Says {Thus has the Word of your Lord been justified against those who disbelieved, that they will be the dwellers of the Fire.} [40: 6].
There are many other clear texts proving this fact. You also explain to them that they are exposing themselves to great danger because by taking a mediator between them and Allah, they believe that they are intercessors with them and Allah. This is the same faith of the pagans during the time of the Prophet Mohammed (Peace and blessing of Allah be upon him). Allah Says (interpretation of meaning): {And they worship besides Allâh things that hurt them not, nor profit them, and they say: "These are our intercessors with Allâh." Say: "Do you inform Allâh of that which He knows not in the heavens and on the earth?" Glorified and Exalted be He above all that which they associate as partners with Him!} [10: 18]. Allah Says (interpretation of meaning): narrating their claims {"We worship them only that they may bring us near to Allâh." Verily, Allâh will judge between them concerning that wherein they differ.}[39: 3].
We would like to draw your attention to an important point that Du'a is a pure form of worship as it is understood from the above Ayah. The Prophet said: "Supplication (du'a) is itself the worship".
As for what they get by visiting shrines it is nothing but a kind of respite from Allah. And there is no evidence that Allah accepts the mediation of those people who are dead and buried in graves. To the certiorari, Allah makes it clear that this behavior is fruitless and blame worthy!! No bearer of burdens shall bear the burden of another (39: 7) who is he that can intercede with Him except with His Permission? (2: 255).       Allah knows best.