Is it permissible for a wife to delay Hajj due to the presence of young children who might be harmed, given her husband's intention to take them for 'Umrah annually?

Hajj is a pillar [of Islam] and an obligation, which, according to the majority of scholars, becomes immediately incumbent upon the one who is able. Whoever delays it after having the ability is sinful. A wife must not delay Hajj, and any potential harm to the children is not a preventative factor unless they require childcare and no one is found to look after them, or if there is a fear of their perishing. The intention of taking the children for 'Umrah (definition) every year does not justify delaying Hajj after having the ability.