Hello and thanks for the information.
You are in a difficult position. There is no legal right as such to know the address that the children stay with their father, but it is often a negotiating point when a couple split up at the stage when contact arrangements are first being discussed. For example, the parent that the children live with could say that there should be no overnight contact with the other parent until they know definitely where the children stay when they are with the other parent. But in your case, the children have been staying with their father for the last 6 years. You must have been satisfied over the years that the children were happy to stay with their father, and were safe with him, and were properly looked after by him, or you would not have allowed the arrangement to have continued for so long.
The argument for having the address is the safety argument - that if anything happened, you would not know where the children were - but children of the ages of 10 and 12 will know the address that they stay at, and they will know your telephone number.
I agree with you, that you should have the address (and his current mobile number) - but the only way to force the issue is to stop overnight contact until you are sure you have been given the correct address - but you need to consider the effect on your children if you do stop them from staying overnight - although their safety is more important than their annoyance IF their safety really is at issue. You should definitely NOT stop all the children's contact with their father, as they need to be able to see him on a regular basis - even if they do not stay overnight - so you could suggest that their fortnightly contact with him change to - say - 10am to 6pm on Saturday and 10am to 6pm on Sunday - until you have the correct address.
You could also consider making an application to court for a defined contact order, asking the court to make an order that specifically states that overnight contact will be resumed only when you have the correct address - but I cannot guarantee that the court will agree that the safety angle is so strong that overnight contact sohuld stop until you have the address. You also need to be aware that going to court is stressful, time-consuming and expensive, so an application to court should only be considered as a last resort.
Instead, I strongly advise you to consider going to mediation, which is a round-the-table discussion with a trained and neutral mediator. Here's where to find a local family mediation service:-
The fanmily court anyway now requires the parties to have attempted mediation before it will consider an application to court.
The children's father might be more cooperative if he gets a solciitor's letter letting him knwo that you are consdering a) stopping his overnight cotnact and then b) going to court if you don't get his address - so here's where to find a specialist family law solicitor for some face-to-face advice, and a letter to him:-
I hope this helps and I wish you the best of luck.
Thanks and best wishes...