Why is VAS performing so poorly

Well I guess it’s all in the title, have been investing some money for my children so it’s for the longer term, VAS is 40% share of the total invest and it was selected for its safer consistency and not the volatility of some of the other ETFs selected. But it’s performance over the last 18months has not been the greatest and thinking of moving to another ETF with similar attributes but better performance anyone else thinking the same ?