@Base248 hi there, this is covered in the Toddler Stuff pack. I attach a Sims Community guide. There's a lot of playground items for toddlers but it needs a big backyard for some things. They are available in smaller pieces though, like slides and ball pits.
https://simscommunity.info/2017/09/15/sims-4-toddlers-park/
There's more things in Growing Together for our littlest Sims too, like splash pads that can be arranged however you want them.
But I think (if I remember correctly 🤔) toddlers can splash in ponds. So you can use your water tool to make a little shallow backyard kids pool and they can play in it and that doesn't require adding content to the game. I just looked up sand pits as well and you can also make one of those with terrain paint, it looks like you need Island Living installed first.
I found a great tutorial here to create a toddler space with a little playhouse too, they've used fountains from the base game to create a splash pad:
https://simscommunity.info/2017/04/18/toddler-spring-playhouse/
I'm just redeveloping a street in Newcrest with a roller rink and shops and I've got a couple of lots left to do. So now I know exactly what I'm going to build, I feel like designing a kids park...that's my afternoon sorted 🎠!