How to make punch at slughorns party? PLEASE HELP 3 yr old is cryn daily

i feel pretty dumb but I cant get past the part where u have to make punch for the christmas party. It has a picture of 2 bottles,i believe,and says shake? it and pour till it turns blue. My 3 yr old and I have tried everything we can think of but just cant get past this ingriedient.Please,Please,Please help us!!!! He is getting a little impatient and wants to play it every time cause he loves Harry and his games.Also is the lego Harry potter games worth buying for the kids? Thanks sooooo much!!!