Why are my child’s teeth like this?

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My DC is 6. Adult teeth are present now in the mouth. We brush twice a day. No sugar overload, a varied balanced diet. However, the teeth almost look uncared for. They are so yellow looking and the adult teeth have been in for a good few months. There’s a yellow spot(hard to see on photo) that’s on her front tooth too. Brushing techniques seem all good so I’m so unsure why this is. Not due a check up for another couple of months but just thought I’d ask advice in the meantime.
Thank you!

What am I missing? They look like normal teeth to me. 🤷‍♀️

I'd go to the dentist earlier if you can, as there seems to be a range of answers

We suspect some is just staining so we want to try that first. Very happy to pay private.

Her molars are very stained, she's had fissure sealants put on some of them. I am anticipating just ripping everything out and getting implants once she's older tbh!

Tooth buds form in the womb but the enamel on permanent teeth forms up to around 7 years old.
Fluorosis can occur any time during this period

This is on the incisal 1/3 of a lower first incisor , the enamel here forms mostly in utero and first few months of life. It’s the wisdom teeth enamel which form later on in childhood as teeth form in a conveyor belt fashion.

No water in the U.K. has enough fluoride to cause fluorosis, tooth brushing will not start until first baby teeth come through 6 to 9 months old and it would be very difficult to feed a baby enough toothpaste to cause fluorosis ,brushing only a couple of teeth , but by this age the enamel at the tip of the first incisors has mostly formed.

Any problems on first incisors and molars are much more likely to be MIH which affects 1 in 8 people to a lesser or greater extent.