40,000 smackers? You want it to turn into 120,000?
Get thee to a lawyer. Yesterday. Your ex is stealing from you. He has essentially stolen as much as a lot of people make in a year. If he had taken 2 brand-new cars from you, you'd be calling for his ass to be hauled to jail.
If he feels the amount is excessive, then his remedy is in the courts, and not in playing on your sympathies. Same with you getting the money from him; he has proven his is thoroughly unreliable in terms of getting this done, so you will need to go to court in order to enforce things.
Will your kids be heartbroken? I dunno. Isn't it better that they have shoes, savings accounts, food, a roof over their heads, and college educations and all of the other things you could do for them with those kinds of simoleans? And isn't it a good idea to teach your children that defaulting on their obligations and not taking care of their own and breaking your promises leads to consequences?