This project is by Randi of Swoon and posted at Dot Coms for Mom's. She used alphabet ice cube trays and ready mix cement. She turned hers into magnets, but you could also just them decoratively on a shelf (perhaps to spell your child's name). You could paint your finished letters, dye the concrete before it hardens or even add glitter.
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(Image: Randi for Dot Coms For Moms)