Sleep Association Disorder: This condition is characterized by the inability to fall asleep or return to sleep without a specific association, such as a parent's presence. The boy's need for his mother to join him in bed to return to sleep after waking up at 1:00 AM fits this diagnosis. It's a common issue in toddlers who develop sleep associations that are difficult to break.

Limit-Setting Sleep Disorder: This could be considered if the child's waking up and demanding parental presence is a result of inadequate limit-setting by the parents, leading to a learned behavior.
Stressor-Related Sleep Disturbance: If there have been significant changes or stressors in the child's life, this could contribute to his sleep disturbance, making it hard for him to return to sleep without reassurance.

Sleep-Related Anxiety Disorder: Although less common, anxiety about sleep or nighttime fears could lead to similar symptoms. It's crucial to assess for underlying anxiety issues.
Underlying Medical Conditions: Conditions like sleep apnea, restless leg syndrome, or gastrointestinal reflux could cause nighttime wakings. Identifying and treating any underlying medical issue is essential.

Advanced Sleep-Wake Phase Disorder: This is unlikely given the child's age and the nature of his sleep disturbance. It typically involves a consistent advancement of the sleep-wake cycle.
Confusional Arousals: These are characterized by disorientation and confusion upon waking, which is not described in the scenario provided.
Chronic Insomnia: While insomnia can occur in children, the description provided suggests a more specific sleep association issue rather than the broad diagnosis of chronic insomnia.