Is an au pair our best option?

18 months with an au pair

Definitely not.

You need a full time nanny who provides wraparound care or a nursery that provides similar alongside a cleaner.
I'd recommend 2 x per week for fewer hours (4 or 5) for the cleaner as your nanny/cleaner in Singapore will not have been cleaning 1 x per week but will habe been doing little bits to keep on top of things throughout the week meaning and you probably won't be happy with the a true 1x p.w. clean

Nursery costs where I am are £60 a day ish.
Cleaners are about £12ph.

Not an au-pair- they’re teenagers here to learn English and give you a hand, not as a cheap nanny/house keeper. Much better for older kids who just need someone around. You need a cleaner and then either employ a nanny or find a nursery. Nanny’s don’t clean. Nursery’s rarely do beyond 8am-6.30 pm so that may be a consideration too. I have to say some returning expat friends have had the worst experiences with sorting childcare because they have had such cheap nanny/housekeeper experiences overseas, and don’t expect to pay for services here. Childcare costs so much- don’t expect a teenager on £100 a week to do it.

Nursery/nanny plus cleaner. As has been said, you can get nanny-housekeepers here but they are relatively unusual.

Au pairs don't do sole all day care of preschool aged children. They are really for wraparound care and occasional evening babysitting. If you want someone to care for your child all day you need a nanny, unless you use a childminder or nursery. But long days and unsociable hours will probably mean you need a nanny. As PP say you're unlikely to find a nanny-housekeeper in Scotland, so you're probably looking at a nanny and a separate cleaner.

Au pairs don’t look after children that young.

Minimum age is 2, and even then most people prefer to use au pairs for older children.

Tbh I doubt that in a few months many au pairs will be keen to come to Scotland - or will be allowed to. Lockdown will still be in force, at least partially.

I gather Singapore took a very strict approach early on so hasn’t had much trouble with covid 19? Are you up to date with the position here?

In general it’s much harder to find nanny-housekeepers here. They are available in wealthy areas, but unusual elsewhere. Most childcare professionals here will clean up after the child a bit (some more than others), but won’t do anything that is general housework or for the parents.

Most affluent working parents use childcare (nursery, childminder, or nanny) and then a separate cleaning service.

Costs will depend a lot on where in Scotland?