I agree with the 'get rid' idea.
You are definitely on the right track by taking the toys away, but since they don't seem to get the point then the consequence needs to 'sting' a little more. Since they're 6 and 7 clearly they are old enough to be responsible for cleaning up after themselves.
Start on Monday by stating the 'new rules' to your kids (you need to be fair and let them know change is about to occur). Let them know exactly what will happen if they leave the pieces/toys out. Tell them that the toy will be thrown away for good - and follow through by taking it to the garbage or donating it as someone else mentioned. Will they cry and scream and mourn the loss of the toy? Oh you bet they will. When they do, acknowledge their frustration only once and ask them "do you know why mommy had to throw away that toy?" (because we didn't put it away, because my baby brother could get hurt if he found it) "what could you have done differently in order to make the toy not go away?" (do a better job of cleaning up), and end it right there. If they continue to tantrum, ignore it. Do not continue to explain, give attention to, or justify your actions.
Good luck to you!