uk – Different travel dates to D-Tier 4 (General) Dep. VISA Partner and Child Level 4 (General)

My wife and daughter had applied for a UK Level 4 dependent visa in the UK. VISA was issued, but the date allowed in their visa differs because my daughter, barely four and a half years old, can not travel with her mother. My wife got a visa for the date prior to her trip but my daughter was given the date. Both applications had the same date filled in the travel information section of the visa form. Although we have received documents today, my wife's visa has a validity of 20 days only from the previous issue date. What should I do in this context?