If you're really bloody organised, or just a better mummy than me, do one layer, freeze and then trip over a few more toys the next morning and do another layer.
Grab salt, some sort of brushes, warm water and syringes. Not with needles in, just, you know, the dropper type.
Once children are over the fright of their toys trapped in ice (oh yes, there were tears!), tell them that really truly, they can get the toys out. They just have to work at it. And it may take some time. Don't let them east too much of the salt.
Meanwhile, you can read a magazine in peace. Summer holiday fun. Love it!