I think we Should do a craft day and Mass produce some of these Rubber Door Mats pressed into a concrete mold and later removed, to make stepping stones. There are lots of other smart concrete project ideas on this page.
DIY The Retreat Garden Bench - Instructions are on another site, in Spanish, but if you are fluent - or don't mind taking the time to translate - it's worth it! BPM Collections-Yard/Garden Ideas,Chicken Coops,Decor and D
Not with concrete, but maybe clay? Get the children involved with these cement stepping stones! All you need is some cereal boxes and quick drying cement. Decorate with glass stones. Excellent idea for the kids to get their garden creativity flowing!