I am one of the people who advise against asking SS for help. Once they get involved and start giving "help", when you decide you have had enough of their "help" they don't stop helping. It seems that Scotland have a more helpful SS than England. I hasten to add that the people I assist in court are usually trying to get their life and children back and I am more exposed to the unhelpful side of SS. One clear and reoccurring point that I hear is that if the parents (the ones I assist) that if the parents had their time over, asking SS for help would not be considered.
At the moment, there is no contact happening. The OP wants contact to happen. The contact that does happen is upsetting the children. There appears to be more than one child.
If the ex wants you to ask him to "walk away". I would avoid asking him to go - purely because you open yourself to being set up. What you should reply is that you don't make adult decisions for him. He should make his own decisions.
Lets assume there are 2 children (for arguments sake). One child is unhappy ad the other isn't. Could one child have contact and the other not. Stress that this is just a temporary arrangement to the ex and the children. There is a likely perception of double standards and differential treatment going to be raised. The counter argument is that contact (where possible) should happen.
Communication is a key component in forming any agreement. If the parents can't communicate, mediation is usually a next step.
In trying to communicate, you want to be clear and try to show that you can see the other side as well. If the other side feel that they are being considered, the conflict has opportunity to reduce.
Explain that the contact as it's happening is causing the older child to not want contact, which is a growing problem for you because you want the child to have a relationship.
Explain that you don't want to dictate the details of what the ex does during contact but you do want to try to assist in the children not being upset and in turn not wanting contact. If the contact works - everyone should be happier.
There are several steps to this process.
You want to establish that the ex is not going to walk away. No point starting a process of negotiation if the man walks away. He should make that decision though. It might be a good idea to ask if he would object to you forwarding copies of school reports, letters and photo's. It's the minimum you can offer and he can choose to decline.
If the man decided to stay in the picture. Aim to identify the issues from the older child's perspective. See if you can offer practical suggestions as an option.
You used the fight situation as an example and I am guessing that your ex likes to play fight with the child. Sensitive children tend to want to avoid fighting.
About 5 years ago, I was writing a statement for a dad who had an obstructive ex who refused contact (long story short) the dad and child (4 years old I think (at the time))playing "fight" was an issue. The solution there was getting the child a blow up hammer (the kind you find on the beach) and him and the dad played by hitting each others foot. The child found this funny and the child's laughter caused the mother to feel less obstructive. It was clear that she wasn't happy because more issues suddenly became a problem and the CAFCASS reporter cottoned on (by some miracle).
The ex wants to play rougher and isn't involved with the child on a day to day basis. Probably not involved with any child on a day to day basis.
The problem with the hammer idea is that someone has to take things further and when it moves to hitting a hammer on someone's head, it gets painful. Clear boundary's here. Only hit a foot because that's funny. Then set a time limit...perhaps 10 minutes so the child doesn't get worn out. If you can set the child up and used to playing a "hammer" game, you have the option of explaining the game to the ex and him playing the same game to get contact started again.
Communication is important here.
Keep accurate and detailed records of what you say to the ex and his reply. Better yet, use email or written letters. Written communication can be referred to again.
If court is inevitable, you have a solid track record of promoting contact and making suggestions. You have the ex's responses. The evidence speaks for it's self and you are in a stronger position to invite someone to better your attempts with a suggestion.
I don't know of more issues (apart from the child getting upset or distressed). Upset is a reaction to something. Aim to solve the problem.
Hopefully that makes sence.