My wife does not allow our 5 year old daughter to play with family boys from above four years.

Answer

Even three year old girls and boys should not play together. Girls should play with only girls. Brothers and sisters may play. But it is not permissible for a five year old girl to play with boys even if they are 4 or 5 years old. The parents who allow their little daughters to play with boys or boys with girls, are opening an avenue of fitnah. Your wife has better understanding than you despite you being the male. She is not 'too strict'. You should view the matter from the Shariat's angle, not from your customary lifestyle.