As Bramwell says, there isn't a lot of talking going on when you play hide and seek. If she knows the game, you can initiate it by just saying 'Let's play hide and seek'. If she doesn't, you can explain it by saying "I'll close my eyes and count to ten. You go and hide, and then I'll come and find you" or the reverse. I think that American English might dispense with the 'ands' in that sentence ('go hide' and 'come find' ) but perhaps an AE speaker could confirm this. The traditional signal for the 'seek' part to begin is when the seeker calls 'Coming, ready or not!'. A variation, which works if there are more than two people or if the search isn't genuine ( i.e. if you know perfectly well that your daughter is under the bed!) is the 'getting warmer' game. As you approach the place where you think she is, you call 'Am I getting warmer?'. This generates lots of useful vocabulary to do with gradations of relative 'heat' as you get closer or further away from the target. As you approach, the hider (or any onlookers) can say 'Getting warmer...getting really warm...getting really hot now... boiling hot!'' or as you move away from the target, the response is 'Getting cooler...getting cold...you're freezing!' or similar expressions. Happy hunting!

Not much really needs to be said, the one hiding keeps quite so as not to be detected. The finder, at the start, covers their eyes and loudly counts up to whatever number had been agreed and then announces that the search has commenced e.g. "One, two...ten, here I come, ready or not!" On discovering the hider, the seeker simply says "Found you!" Children's games very slightly from place to place, but the version I play with my daughter, and played myself as a child, does not have any special vocabulary.