This was requested by @Emilynappi

''Mycroft, I'm back!'' You shout as you shut the front door of your boyfriend's mansion. Rosie was giggling and playing with your hair as you went to look for Mycroft. John and Mary were desperate for a few days to themselves and asked you to look after Rosie. You happily accepted but you were afraid that Mycroft wouldn't be very happy to have Rosie here. He hadn't met her yet and he wasn't very fond of babies which worried you. You wanted to have children ever since you were a little girl but Mycroft hated babies and made it clear to you that he didn't want children. You dropped the heavy bag filled with stuff for Rosie on the floor and went to the kitchen. Mycroft was busy making tea and didn't turn around when you entered. ''Did you have a good time with Mary and John, Love?'' He asked, still occupied. ''Yes, it was lovely.'' You answered. Mycroft finally turned around with a cup of tea in his hands. He nearly dropped it when he saw Rosie in your arms. ''What's that?'' He said, a disgusted expression on his face. You rolled your eyes and sighed. You walked closer to Mycroft to introduce him to the young Watson. 

''This is Rosie Watson, John and Mary's baby.'' You said, smiling when Rosie attempted to pinch his nose. Your boyfriend took a step back. ''She'll be staying here for a few days. Mary and John needed some time to themselves and asked me to take care of her.'' You explained. ''I don't want a baby in my house! You know how I feel about them.'' He protested. ''I don't care.'' You took Mycroft's cup from him and placed it on the counter. ''Here, hold Rosie for a minute. I'm going to set up her crib in the guest bedroom.'' You handed Rosie to him but he refused to take her from you. ''I'm not holding that!'' He said loudly. ''Mycroft! It's a baby, not a monster that'll eat your face off!'' You argued. Mycroft shook his head rapidly and practically ran to his office, leaving his tea and you behind. You huffed angrily.

You loved Mycroft more than anything in the world but you didn't know if staying with him was a good idea. His plans for the future were completely the opposite of yours and you were afraid that it could cause problems in the relationship. A single tear rolled down your cheek and Rosie raised her small hand and put it on your cheek. She made a funny noise and you pressed a soft kiss on her forehead. ''Thank you, Rosie.'' You said, smiling. She giggled adorably and clapped her small hands together, something she always did when she got excited according to her parents. You went back to the hall to retrieve the heavy bag and made your way up the stairs to the guest bedroom where Rosie would be staying for a few days. You carefully placed her on the large bed and started working on setting up her crib, keeping an eye on her at all times to make sure she didn't fall off.

***

Rosie's loud crying filled the entire house as you tried to prepare some food for her. You were exhausted from taking care of her all day on your own and wondered how John and Mary were still sane. ''I'm coming, Rosie. Your food is almost ready.'' You cooed, trying to calm her. Mycroft entered the kitchen, looking very annoyed. ''Could you keep it down a little? I'm trying to work.'' He complained. You turned to face him, anger radiating from your eyes. ''THIS WOULDN'T BE SO HARD IF YOU JUST HELPED ME OUT A LITTLE!'' You yelled. Mycroft was a little surprised, you had never yelled at him before. ''I'm too busy, (Y/N).'' He defended. ''YOU'RE ALWAYS TOO BUSY. NOW, GET OUT!'' Mycroft rolled his eyes and went back to his office, feeling a little guilty for not helping. He just didn't like babies and didn't know how to take care of them but he had to admit, you looked insanely beautiful when you interacted with Rosie. He smiled slightly to himself and went back to work.

It was getting really late and you were beyond exhausted. Baby Watson still hadn't fallen asleep and you tried everything. You put her in her crib causing Rosie to start crying again. You sighed and picked her up again. ''Stop being so difficult.'' You whined. You started to seriously doubt having children in the future. You gently rocked Rosie and sang lullabies until she fell asleep. You smiled as you put her back in her crib. ''Sweet dreams.'' You whispered. You headed to the bedroom you shared with Mycroft and fell on top of it. Mycroft was already asleep. You quickly changed into some comfortable clothes and got into bed next to him. He wrapped an arm around your waist in his sleep and mumbled something you couldn't hear clearly. You covered yourself with the duvet and immediately fell asleep.

***

Mycroft instantly awoke when Rosie started crying again in the middle of the night. He looked at you and saw that you were still asleep. He still felt slightly guilty for not helping you and decided to calm her down himself. He carefully got up from the bed and went to the guest bedroom where Rosie was staying. He gulped as he approached the crib. He had seen you calm her down a few times and decided to just copy you. He hesitantly picked the crying baby up and held her in his arms. ''It's all right. Tell me what's wrong and I'll help you.'' He said, rocking Rosie in his arms. She kept crying and Mycroft didn't know what to do. Mycroft still remembered a lullaby that he sang to Sherlock when he had trouble sleeping as a kid. He didn't know what else to do so chose to sing that to Rosie. ''Hush-a-bye, don't you cry. Go to sleepy little baby. When you wake, you shall have all the pretty little horses.'' He sang softly. Rosie's eyelids started to droop a little and her loud crying was replaced with silent tears. Mycroft smiled and continued to sing, ''Blacks and bays, dapples and greys. Go to sleep, you little baby. Hush-a-bye, don't you cry. Go to sleep, you little baby.'' He stopped singing when Rosie's eyes shut and she fell into a peaceful slumber. He put her back into her crib and pressed a kiss on her small forehead before returning to the bedroom.

''(Y/N)?'' Mycroft whispered, gently trying to shake you awake. You hummed and opened your eyes slightly. ''What's wrong?'' You wondered. Mycroft smiled and wrapped his arms around you, pulling you tightly against him. ''I want to have a baby.'' He whispered. You smiled and snuggled even closer to him. ''What changed your mind?'' You asked sleepily. ''Seeing you interact with Rosie is one of the most beautiful things I've ever seen in my life. And I found out that babies aren't so bad after all.'' He explained. You nodded and closed your eyes again. ''I'd love to have a baby with you, Myc. But let's get married first.'' You mumbled against his chest. ''Of course.'' Mycroft replied. He kissed the top of your head as you fell asleep again. He knew exactly what he would ask you in the morning.

Hope you liked it ♥