Lamaze Peackock Toy
Lamaze baby products have a great reputation with babies and parents, so it makes sense that Lamaze toys make great diaper cake ideas. This set of baby items works well for a boy, but using slightly different colors in the blanket could also create a great baby girl diaper cake.
Visualize the peacock as the top of the diaper cake. If you’re doing a two or three tier cake and want to cover it with fabrics to hide the diapers, blankets, onesies and bibs work perfectly.
Lamaze toys help babies learn by providing a mixture of textures, sounds and colors. This toy has a mirror, crinkly tags, and squeaker toys. It comes with a link so it can be attached to a stroller or high chair without getting lost.
There are lots of colors to work with in this toy which makes coming up with ideas for accessories to add so much easier. You could play off of the yellow and red for a girl diaper cake or even keep it neutral with greens and yellows.
See the suggested supply list here: 
Blue Polka Dot Baby Blanket
Red and Blue Pacifiers
Deep Blue Infant Bodysuit Set
Red and Blue Feeding Spoons
Red White Blue Infant Sock Set
Green and Blue Grosgrain Ribbon
The patterns also keep things very interesting. I chose diaper cake decorations in solids and polka dots but stripes or swirls mixed with solids would work well, too. I also tried to reduce the cost of the diaper cake and yet still make it fun. The Lamaze toy costs just $9.99 on Amazon at the moment but provides lots of interactive play options and will last for a long time. The blue outfit was probably the most expensive but you could replace that with a blue bib or leave it out entirely if the blanket is sufficient to cover the size of your diaper cake.