I thought only
Jacob Rees-Mogg brought his nanny everywhere!!!
Joking aside, there isn't a nanny or an au-pair visa for the UK. To the best of my knowledge, there used to be one, but that was discontinued when we joined the EEC because most of our au-pairs used to come from France and the rest of the EEC anyway.
Here is a
page on the Gov.UK website about au-pairs, who are essentially child-minders who stay with the family.
Keep in mind that in the UK, they do acquire rights under labour laws.
I'm not sure that you are eligible to be an employer for a overseas domestic worker visa as mentioned by
@JB007, because you are neither a British citizen or a foreign citizen who intends to remain in the UK for no more than six months. If the latter is true, your Skilled Worker visa is at risk.
You may want to look at checking with the local council in the area that you plan to live in, about schooling for SEN (special educational needs) children. Or work out a way for the children to stay in Singapore, though that will negatively impact any chance that they may have to move to the UK.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.