It is a well known fact that the 19th century mystic saint Ramakrishna Paramahamsa practiced other religions apart from Hinduism. Well known examples are Christianity and Islam (particularly Sufism). However, do any of the biographies of Ramakrishna Paramahamsa indicate that He accepted Jesus Christ as the begotten son of God?
According to Sri RAmakrishna, Jesus Christ was an incarnation of God. So, an incarnation and not a son.
I am quoting from the Bengali version of the book "A short life of Sri RAmakrishna".
Seven years later he had a similar realization of Christianity. In 1874 Sri Ramakrishna came into intimate contact with Shambhu Nath Mallick of Calcutta, who had a garden close to the Dakshineswar Kali temple. Sri Ramakrishna used to spend a good deal of time in this garden-house of Shambhu Mallick, who came to regard the Master with sincere love and esteem, and after Mathur’s death gladly supplied all his wants. Though not a Christian, he used to read the Bible to Sri Ramakrishna, who thus came to know about Christ and Christianity. He felt a strong desire to realize the Divine Mother by this new method, and it was fulfilled in a strange way. One day Sri Ramakrishna was sitting in the parlour of a neighbouring house belonging to Jadulal Mallick, a devotee of the Master. On the walls were many beautiful portraits, one of them being of Christ. Sri Ramakrishna was looking attentively at the picture of the Madonna with the Divine Child and reflecting on the wonderful life of Christ, when he felt as though the picture had become animated, and that rays of light were emanating from the figures of Mary and Christ and entering into him, altogether changing his mental outlook. When he realized that his Hindu ideas were being pushed into a corner by this onrush of new ones, he tried his best to stop them and eagerly prayed to the Divine Mother, ‘What is it that Thou art doing to me, Mother?’ But in vain. His love and regard for the Hindu gods were swept away by this tidal wave, and in their stead a deep regard for Christ and the Christian church filled his heart and opened to his eyes the vision of Christian devotees burning incense and candles before the figure of Jesus in the churches and offering unto him the eager outpourings of their hearts. For three days those ideas held sway in his mind. On the fourth day, as he was walking in the Panchavati, he saw an extraordinary-looking person of serene aspect approaching him with his gaze intently fixed on him. He knew him at once to be a man of foreign extraction. Sri Ramakrishna was charmed and wondered who he might be. Presently the figure drew near, and from the inmost recesses of Sri Ramakrishna’s heart there went up the note: ‘This is Christ who poured out his heart’s blood for the redemption of mankind and suffered agonies for its sake. It is none else but that Master Yogi Jesus, the embodiment of Love.’ Then the Son of Man embraced Sri Ramakrishna and became merged in him. At this the Master went into Samadhi and lost all outward consciousness. Thus was Sri Ramakrishna convinced that Jesus Christ was an Incarnation of the Lord.
From, the 17th chapter of the aforementioned book titled " Practice of Christianity and the story of DAkAt BAbA"
As an additional info, Sri RAmakrishna believed that Buddha was an incarnation of God. But as far as the Jain and Sikh Gurus are concerned, then as per him, they were not God's incarnations. And, as regards the 10 Sikh Gurus, then he believed them all to be King Janaka's incarnations.
From the same chapter:
It will be worthwhile to note here Sri Ramakrishna’s opinion of Buddha and other great founders of religion. About Buddha he shared the general notion of the Hindus that he was an Incarnation of God. He used to offer him his sincere devotion and worship. Once he remarked, ‘There is not the least doubt about Lord Buddha’s being an Incarnation. There is no difference between his doctrines and those of the Vedic Jnanakanda.’ We have every reason to believe that he spoke thus because of his supernatural insight. About the Tirthankaras who founded the Jain religion, and the ten Sikh Gurus, Sri Ramakrishna heard a good deal in his later life from the lips of representatives of those communities and came to entertain a great regard for them. In his room at Dakshineswar there were a small statue of Tirthankara Mahavira and a portrait of Christ, before which incense was burnt morning and evening. Of the Sikh Gurus, he used to say that they were all incarnations of the saintly king Janaka.
Well it's a known fact that Ramakrishna Paramahamsa practiced other religions apart from Sanatan Dharma as we can read below:
Ramakrishna was initiated into Sanyaas or formal life of an ascetic during 1865 from Monk Totapuri. Totatpuri guided Ramakrishna through the rituals of renunciation and instructed him the teachings of Advaita Vedanta, Hindu philosophies dealing with non-dualism of spirit, and importance of Brahman. It was now that Ramakrishna attained his highest spiritual realization.
In the subsequent years, he undertook practicing of Islam, with observing all the rituals of the religion in a devout manner. He even experienced vision of a radiant white bearded man. His tryst with Christianity came much later, in 1873, when a devotee read The Bible to him and he got immersed in the thoughts of Christ. He had a vision of Madonna and Child and of Jesus himself.
But that was a very well thought out process just to make common people understand some simple things about different religions.
The ultimate motive:
He directed that the ultimate goal of every living soul is God-realization. Having practiced different facets of Hinduism as well of other religions like Islam and Christianity, he preached that all of these religions were different paths that lead up to a single goal – God.
So if you read everything clearly it never states that he accepted Jesus Christ as the son of God, because that was never the motive behind what he did.