It is important for a child to have a relationship with both parents, and it is their right. However, if your child is suffering emotionally as well as physically as a result then it is your duty to ensure your child is protected. Don't feel bad about the decision you made but do try and find a way to resolve it. This issue is not going to go away, your ex can get lots of help with how to handle things in court, even if he can't afford a sol, and the court will likely insist on some form of contact. So you need to do what need sto be done to ensure your son is safe when that contact happens.
While your son is with his Dad it is not for you to dictate how he is cared for, who he sees and what he does. It is a hard thing to accept I know, especially if your Ex's family is very different to the kind of situation you know and prefer.
Think about this though... when your son is with you do you ever leave him with your parents, or a babysitter or neighbour? Do you tell your ex where you are taking him whenever you go anywhere, what he has eaten and who he has seen? No, because what you do in your time with your child isn't his business. There is nothing wrong with your Ex also leaving the child with his mother or other responsible person and in making decisions about how he is cared for and what he does. In fact it would put my mind at rest on some level knowing his grandparents were around to monitor things, and that Gran is ensuring your son (her grandson) is taken care of.
How about writing to your son's Gran saying that he has asked to see her and would she be prepared to come and visit him at your house for an hour, or to meet at the park/zoo etc. Keep that seperate from visits with his father at this stage. It would help her see you are trying to be reasonable and are considering your child. It will also show the court that you are not trying to stop your son having a relationship with his father and family, just that you are trying to ensure he is safe when in his father's care.
Speak to the school, to the head but also your child's class teacher. Ask them if they have noticed any significant changes in your child's behaviour since his initial problems, ask them what they attribute it too. Children do sometimes find school hard to adapt to at first, especially only children who have never had to compromise and deal with others. Ask them if they have any concerns about child at this stage. Also ask if they think it would be good for your child to speak to a child psycologist. This might help deal with some of the issues and help your child speak about any problems or concerns he has.
Different families have different methods of disciplining. Children can adapt to two homes with two different sets of rules, just as they adapt to school having different rules. While i do not believe in smacking, plenty of people do. But this should be a small tap on the bottom, hitting around teh head is very dangerous. Perhaps suggest to your ex that he should go on a parenting course to help him find non aggressive ways to deal with behaviour he finds difficult.
If you are worried about his temper ask that he, and even his parents if he wants the child to go to their house, go on an anger management course. Ask for an undertaking that he will not smack your son as a form of discipline in future, and try and get his agreement that smacking around the face is harmful and somethign he will no longer do.
The mediator will only be as good as the people they are trying to help allow them to be. Don't be afraid to say what you want and how you feel and why things are difficult. Do be open to suggestions and
advice on how to reach agreement, but don't agree to something you don't intend to go along with. Ask the mediator to help find ways of tackling the issue of your Ex not liking your son's thumbsucking as this seems to be a problem your son has spoken to you of. Try and get that verbal agreement that smacking will not occur, and that smacking a child around the head is not acceptable.
If Ex wants you to agree to him seeing his son at his home again then he will have to show that he can be responsible. He might say it's un-necessary, but state that it will put your mind at rest for him to do these things and will be beneficial to your son in the long term (ie anger management and parenting classes).
Speak to the mediatior before you go again. Say that you felt/feel very intimidated and that you are looking for a solution and have only taken the action you have because you believe it is right for your child's safety and emotional welfare. Ask that they support both of you through this. Make it clear that you want what is best for your son and by being at mediation you are showing willing in finding solutions.
Take a list of questions with you when you go again. Ask the mediator to help you both find solutions to your issues, such as getting your ex to agree to the parenting classes and anger management course. Also say if you are willing for grandmother to see child as son has asked for her, but explain why only grandmother at this stage and how ex should look at all this as a positive step forward. Ask him to work with you to resolve the issues and show that he is willing to meet your requests which will help you trust him more than he is willing and able to be a responsible, caring parent,
Remember, any agreements made at mediation are not binding, and can not be disclossed to the court. If your ex is unwilling to compromise, and do what you ask and put's a stop to teh mediation do try and get a letter from the mediator saying that mediation has broken down as a result of your ex. This you can use in court. However, bear in mind your ex could also get a letter saying the same about you if you are the one not willing to find solutions.
Another thing to consider is a contact centre. The staff at these centres are very good, and it can be a positive step forward to a starting place for contact to resume. You can agree to some of these sessions being just dad, and possibly allow his to take the child out of the centre if his mother accompanies.
There are lots of options. Use the mediator to help you, don't be intimidated by them, and don't be afraid of telling the mediator you feel intimidated or stressed and asking for a 5 minute break during the mediation.
Good luck, let us know how it goes
Gilly