We really live in a VERY unfair world dont we?
My situation was similar but reversed. We didnt want my son seeing his mother who blatantly told us that she really didnt want to see him, but was doing it to wind us all up!! - denied saying it in court though!
BRISOLGUE, get your b/friend to seek legal advice as soon as possible. If his children are becoming distressed by being held back, then the court can instruct a CAFCASS officer to become involved and get to the heart of the problems.
It might even be just the scare his ex needs to stop being silly and allow contact.
Does he pay maintence through an aggreement with the court or CSA or off his own back. If its the latter, suggest he sorts it out via CSA - he may have to pay more or less, but the courts look on this in his favour. Also, keep a record of payments made and for how much and how paid.
Keep a diary of whenever he sees his ex and how the meeting / conversation / children behaved went. this will help with your solicitor.
above all, good luck
Flower xx