Deed of covenant to stop you changing your Will?

Dear all, just a quick question, with some long answers requires I am sure! A couple are divorcing, and the other side have proposed as part of the split, to enact a deed of covenant each, which basically states they can not change their Will in the future, and their assets must go to their children. Has anyone come across the successful implementation of this? Both sides would have to agree to this.

I see a few issues, namely will it circumvent the Wills Act if they get married in the future? Will it have to stop them disposing of their estate? Maybe they could create a trust as the new owner, so those assets no longer follow the Will. It appears to be a minefield, but I look forward to anyone who has dealt with this before!