Shady Oaks Butterfly Farm gives free eggs for anyone wanting them. Of course, you have to pay the shipping, which I'm not sure offhand what that would be. I've included the link below.

I'm not sure if anyone else gives eggs or not. You could do a search on "Free butterfly eggs" or something like that and see what comes up. Good luck.

Here is a link that might be useful: Shady Oaks Butterfly Farm

Shady Oaks is very reputable. I've not purchased eggs or livestock from them but have purchased a good amount of larval host plants to attract certain butterflies to my yard.

Perhaps the project can include growing the larval host of a couple of butterflies and then the children could learn about conservation and how and what to plant to attract the native species.

Seems it would be better in the long run if a patch of milkweed (Monarch), cudweed (Painted Lady) or passiflora (various fritillaries) or some other native larval host were planted to ensure they will keep coming back.

Just a thought...

~ Cat