Environmentally friendly, designer cloth, Bunny Butt nappies are for everyday, Pj's, undies and swimwear.
These are for both boys and girls, need no mesh and can be used from base Game on. This is the Maxis nappy with a makeover.

The Maxis Nappy/Diaper has been with us since Base Game and it surely looks like Base Game content in regards to the texture.

When I found this cloth diaper/nappy by StrangeTomato https://strange-tomato.livejournal.com/336249.html I knew I needed to make some recolours. I wanted a more matt appearance and more prominent press studs, so the pds has been tweaked with a retexture by gdayars and I added more texture to the press studs in Corel Paintshop.

The game has a funny mechanism for buying and setting toddler clothes. In the vanilla game your sim can buy toddler underwear but not set them or wear them as underwear or swimmers. So any nappies you buy will show up in everyday and pj's only.
To open up the underwear and swimwear category you will need a mod like Pescados Clothing tool http://www.moreawesomethanyou.com/ffs/al/hacks/ or Insimenator that allows toddlers to plan and wear undies and swimwear.

One way you can make your toddlers change into undies or swimmers is to use Echo's pool. You will still need to set them first.

celebkiriedhel recolour http://modthesims.info/download.php?t=532799# of Echo's paddling pool http://modthesims.info/download.php?t=327949shown here.
You will notice some strange dark areas on the nappy straight on and this happens to the Maxis nappy as well.

Patterns
https://www.vecteezy.com/
https://pngtree.com/
Corel paintshop


Additional Credits:
StrangeTomato for her Cloth Diaper PDS
gdayars for tweaking the PSD http://modthesims.info/member.php?u=46059