"Meng Meng," "Xiao Xiao," "Duo Duo," "Yuan Yuan" — double-character names are cute as nicknames, but may not suit adulthood.
Cute, memorable, warm. Great as nicknames (milk names) that children hear growing up.
Not formal enough for professional settings. A 30-year-old "Chen Xiao Xiao" may seem unprofessional in the workplace. Double-character names lean feminine, especially for boys.
Use repeated characters as nicknames. Keep the formal given name non-repeated. Or use repeated characters as middle names or English names.