Flowers for a child friendly garden

[AkionTotocha]

Hellebores as well - tough, undemanding & flowers at a time of year when not much else is around. I'm going to stop now before I just start listing my favourite plants

Hellebores have highly poisonous compounds too, for what it's worth.

I think plants that aren't poisonous are better for kids. I doubt they will eat things in the garden, but they might pick flowers and then not wash their hands. (To a kid, a wipe of your hands on your shirt counts as a full antibacterial deep-clean scrub)

Sunflowers, Nasturtiums, Primulas, Lavender, Dahlias, Daylilies (not actual lilies), Snapdragons etc. They're not always delicious (Snapdragons are awful) but they aren't poisonous and they are quite colourful.

Unfortunately, the poisons in plants keep pests away. Almost all of those plants (except for lavender) are tasty goods to slugs, and I think that's the biggest problem you'll have.