Pregos in the Ballyowen Shopping Centre in Lucan(the restuarant is upstairs) dont do an early bird as far as I know but from past experience the grub is fairly good and reasonably priced. Have been there in the past with young children but not very recently so worth checking.
La Banca in the village used to be owned by the same guy who owns Prego's - the menu used to be a more upmarket version of what Prego's serve, but I think it's now been leased out and the menu has gone all "European" and the service is sh%^te.
Da Vinci's in Leixlip is very child friendly - they give them pizza dough, rolling pins etc to play with and they have a good kiddies memu - pizza, plain pasta, bolognaise etc all in kiddies portions. Dont do an early bird however but you get a decent bit of grub at a fairly good price.