Aaggh! Just typed you a list, and crashed. I'll try again, hope there is something that's not too messy for you, and fits the bill:
Easter cards - try sticking yellow circles of paper on, and orange diamonds to make Easter chicks. Or screwed up yellow tissue paper for chicks. Or stick and decorate Easter egg shapes.
Easter egg shapes - cut out of card, and then paint, colour, or stick to decorate.
An Easter egg hunt works well, if you've got a safe outdoor space, where they can search for a long time.
Decorated eggs - sticking tissue paper on with PVA is not as messy as it sounds, and is very effective. Also worth exploring dyeing eggs - if you write on them first with a white wax crayon, the design comes up.
If you get some Easter shaped cutters you can make Easter biscuits to decorate. Or just have an 'Easter playdough' session.
Papier mache plates - to display your decorated eggs on. It's not as messy as it sounds, honest. Tear newspaper into small bits (c. 1" square). Cover plate with vaseline. Then layer of newspaper bits, and paste liberally with wallpaper paste. Three layers. Final layer can be pieces of glossy magazine, to make an artistic effect.
Easter bonnets, of course. Make a simple newspaper hat, then give them lots of things to decorate it.
Flowers made out of tissue paper squares. But 3 - 5 squares together, fold into a fan shape, and tie in the middle, with some florist wire. Then gently pull out the layers one at a time. (Does that make sense? Quite faffy, but 5-7 girls might enjoy it).
I think I'll stop there...