These cups are intended for use with healthy drinks. Water and milk are the best drinks for children of any age. Thick, fizzy or pulpy drinks may block our valves and cause it to break or leak. Also, it is not recommended to fill the cup with hot liquid. To prevent scalding, allow the hot liquid to cool down before you fill the cup. We don’t advise to use formula milk with a spout, only with a bottle teat, as this can clog the holes and cause the spout cup to leak.