I have listed some suggestions for you here - obviously you won't do it all in the one day but may be useful for future reference -
1. Viking Splash Tour - 01 7076000
2. Dublinia - www.dublinia.ie
3. Tara's Palace and Childhood Museum, Malahide [broken link removed]
4. National Sealife Centre, Bray (I know its outside Dublin but you may be travelling nearby)
5. The Ark Cultural Centre for Children, Temple Bar, www.ark.ie
6. Imaginosity, Sandyford, [broken link removed]
7. Dolls Hospital and Teddy Bears Clinic, Sth Gt Georges St
8. Lambert Puppet Theatre, Monkstown - 01 2800974, www.lambertpuppettheatre.com
9. Airfield Trust, Dundrum, working farm, animals, www.airfield.ie
10. National Aquatic Centre, Blanchardstown, www.nationalaquaticcentre.ie