PLEASE DO get your son in counseling. It is awesome how bad things from childhood -- even when kids are that young -- become deep seated and NEED treatment, so as not to cause real problems as he grows older. The "play therapy" sounds good as a place to start, but don't just assume that he will forget the experiences.
I have also seen the power of God to work miracles in healing the psychological wounds of ones who are dear to me. So I really encourage you to get your family involved in a Christian church, and then attend on a regular basis. As your son grows up, this will place him (and all of you) in an environment that exposes you to the forgiveness and grace that are available through Jesus Christ. Once an individual has a relationship with Jesus, then "ALL THINGS ARE POSSIBLE...". If there is any latent psychological damage, this is the best way to begin and complete the healing process. Besides that, church is uplifting and provides access to loving, caring people that can provide healthy friendships. Church can also be a LOT of FUN!
God Bless you and your son,
Matthew 19:13-14 - "Then some children were brought to Him so that He might lay His hands on them and pray; and the disciples rebuked them. But Jesus said, "Let the children alone, and do not hinder them from coming to Me; for the kingdom of heaven belongs to such as these."
Luke 17:1-2 - "He said to His disciples, "It is inevitable that stumbling blocks come, but woe to him through whom they come! It would be better for him if a millstone were hung around his neck and he were thrown into the sea, than that he would cause one of these little ones to stumble."
1 Peter 3:18 - "For Christ also died for sins once for all, the just for the unjust, so that He might bring us to God, having been put to death in the flesh, but made alive in the spirit..."