how about colored real eggs...

It may do if the egg is big enough. A clementine is slightly smaller.

So would dried fruits like figs, dates, apricots, pineapple slices. Or perhaps a bag of mixed fruit-and-nuts (sold as snack food or as cake-mixture addition).

A bit ironical though, putting a sugar-free food inside a food rich in sugar, unless you can make the egg yourself from some chocolate foundation that uses a non-sugar sweetener!

In any case, strictly speaking, there is no such thing as "sugar-free" fruit. Sugars of one type or another are natural components of many edible plant parts, even if not obvious to the taste.

not exactly 'healthy', but sugar-free jolly ranchers are pretty damn good

I doubt clementine orange will fit. Find a good candy maker like Russell Stovers and buy some sugar free candy individually wrapped and put a piece in half of the eggs.

The other half put a note stating “good for family zoo adventure “ or whatever. Some could be a promise for favorite breakfast or nature adventure.

dried figs.
Custard Apple.

Money. 😉💰💶💷

Cheese 🧀😋😁

Mini carrots

Annie's strawberry bunnies crackers

you lost me you want to put a healthy snack inside an unhealthy snack is this a glimpse a peep at your dark side ? 🙃🤔

Vitamin C tablets lols 💃🏻

A toy?

wheat grass
spirulina
a healthy eating guide

You're asking to get jumped by kids 😂