Does a young girl's hand touching my arm during prayer invalidate the ablution and prayer, and necessitate their repetition?

Your prayer is valid, and your ablution is not nullified by touching a woman or a girl, nor is the ablution of the girl who is touched, as long as there is no lust from either of you. If lust is present from both parties, ablution is nullified according to some scholars, while others believe it is not nullified due to the absence of a specific text concerning it.