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Why does my older sister, aged 13, not want to play LEGO with me anymore and stays in her room the whole day? – Beth, age 10, Australia.

I am sorry to hear your 13-year-old sister does not want to play LEGO with you anymore and stays in her room all day. This must make you feel sad and maybe a bit rejected.

It is not your fault. There are many reasons why this could be happening and I can’t say for sure what it is. In this article, I am going to talk mostly about one of the possible reasons that could be involved (but it may not explain everything).

Like many 13-year-old girls, your sister is going through a change in her mind and body called puberty. It may be making her behave differently. Puberty is when your body changes from being a child to becoming an adult.

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What is puberty?

During puberty, a person’s brain and body suddenly starts to produce a lot more hormones. Hormones are chemical messengers that send signals from the brain to body glands.

The main hormones that cause puberty changes are found in two parts of the brain – the hypothalamus and the pituitary. These brain parts make hormones called luteinising hormone and follicle stimulating hormone. The main puberty gland in girls are the ovaries, and in boys it is the testes.

In girls, eggs are stored in the ovaries, which are in the lower belly. The ovaries make other hormones called estrogen and progesterone.

Estrogen and progesterone in girls cause lots of body changes like growing breasts and having periods (bleeding from the vagina) once a month.

Hormones can affect how we feel

The increase in all of the hormones in the brain also affects other parts of the brain to cause some people (girls and boys) to become sad and angry. They might be upset at times or really happy at other times.

As hormone levels go up and down, that can trigger changes in brain chemicals called “serotonin” and “dopamine”. Serotonin and dopamine can change a person’s mood and behaviour. Some people get very moody and feel really irritated by small things that did not bother them before.

Puberty changes in the brain can also make kids start to feel more grown up. Your sister might also look more like an adult woman in her body and feel that she is too grown up to play LEGO anymore. She might want more of her own space to chill out.

But it is important for your parents to find out why she is staying in her room so much – in case she is feeling too sad or actually depressed (which is severe sadness) and wanting help.

What do you do now?

I suggest that you keep being nice to your sister and let her know that you care about her. Try waiting for her to chat to you. Change is tough for everyone. Your sister is trying to cope with the changes of puberty, and you are trying to deal with the changes in your sister.

Most brothers and sisters end up being good friends again – but it can take a bit of time.

Hang in there!

Read more: Curious Kids: Why do people grow to certain sizes?

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