J.C.
I would say this, "I just wanted to let you know that when you are done using the items I loaned you, I would like them back because we are planning on having more children."
Usually when I want someone to keep something I say, "It's all yours, you don't owe me any money and you may do what you want with it."
My sister has loaned me stuff and I have loaned her stuff. When I am done with it, I usually say, "Would you like your items back or do you want me to sell it at our next garage sale and I will give you the money?" I usually end up selling it for her since we both have smaller houses.