Here s the situation, me 16 years oldand my mom is going travelling with singapore airlines and she already brought both of our tickets?

Then my sister 13 years old says she also wanna go. But my mom say that she can't book anymore tickets since she need to book another child that means she need to book a child and an adult ticket at the same time or she must pay extra to make changes so my sis can't go.
what to do I really want my sis to go

Then you reach into your pocket and pay the fare.
Your parent is not an unlimited money machine.

If it is really important to you that your sister go your mother could for a cheaper price change your ticket to her name and you stay home and your sister goes.

Your mother has already told you

This is your mother's decision. She doesn't not have to buy another adult ticket. There really isn't any difference between adult and children's tickets except for babies younger than 2 years.

If it's just a logistics issue with the booking, your mom can call the airline and have your sister's ticket associated with yours. She does not need to book another adult ticket in order to book your sister's ticket.

I think your mom has misunderstood. She is already flying, with you, and has bought (not 'brought') the tickets. So she is established as an adult traveller who has paid for tickets. There will be NO difficulty for her in buying another child's ticket if she just contacts the airline and explains the situation to them. It is not at all unusual or difficult.

Look, your sister can go on this trip, she just needs to pay a bit more for her ticket. So why don't BOTH of you think of some ways to earn some money. You are 16 years old. When I was 13 years old I turned my back yard into a money making machine. I had six hens laying eggs every day. I sold them by the dozen and I sold them by going door to door. I did the same thing with my goat's milk. Then I bought a horse and took people for rides on my horse and they paid me $10 dollars for each ride. I made a fortune. But, if you don't have room for animals then how about starting a sweeping and raking business and offer your services for bargain prices. Offer to clean their whole yard for $20 dollars. Offer to clean their yard for each week at the same price. This way they will never see leaves on their lawn again for as long as your business is there for them. I could give you many other ideas but then you might get confused. Just start a business where you clean their yards by SWEEPING and RAKING. Don't use a LEAF BLOWER because it lifts the dust into the air and it goes into their homes and becomes dust on their shelves and beds and everything else. Never use a leaf blower. In fact you should state that on your flyers. Tell how you never use Leaf Blowers. That alone will get you hired everywhere. Make up a flyer with your business model and leave it at their front door. Start with just your immediate neighborhood and branch out slowly until you have two hundred homes to clean their yards. How much money is that? It is $4000 dollars. That is enough to pay for your sister's flight and all her food in the restaurants for your entire trip. You must go to HOME DEPOT and buy a WAREHOUSE BROOM. Buy a good wide rake that will reach as many leaves as possible and now you have all the tools for your business of SWEEPING and RAKING. Every home will love your prices. You will be hired and making money within minutes.

We have to wonder why your mom would NOT book a ticket for your 13 year old (MINOR) child in the beginning. Was your sister going to just hang out alone at home for a few weeks?

But if for what ever reason your sister now wants to go, your mom needs to contact the airline(or a travel agent) directly. She can't do this on the Website. Yes she is buying a minor a ticket by itself but she is not traveling alone. Once your mom contacts them they can link her reservation to yours and your mom to avoid any unaccompanied minor issues.

You have a weird family😂😂😂

Is your mom going on a sex vacation! With you as her wing girl…