Is Piriton Safe For Children Below 6 Years?

Hi my partner went to the shope to get piriton for our 3 year old shes almost 4 and tall for her age while I was in the bath he gave her a quarter of a tablet when I came out I notuced that it wasnt what I usually buy as I uaually deal with all that it was adult tablets and the box says not for children under 6 im very worried now incase somthing happens??