They're at that age where they want to monopolize their mother.
They're at that age where the want to keep mommy all for themselves.
"ママを独占したいお年頃だよね"
- They're at that age where they want to monopolize their mother. 少し固い表現です。
- They're at that age where the want to keep mommy all for themselves. もう少しカジュアル
8ヶ月くらいの子どもは、ママのことばかり追いかけて、ママを独占したい、そんなお年頃です。
Children around 8 months old ten to chase their mother around and monopolize them. They're at that kind of age.
アメリカ合衆国 
