Hello Kitty and welcome to the forum.

I'm not able to personally recommend anything but for starters or in the absence of any other responses, this link may be of use to you.

https://www.angloinfo.com/lisbon/direct ... garten-586

Maybe a bit late, but very good info for anyone in the future:

I have no official link, but am just so happy we found this place for our daughter and now feel like part of the family 🙂

Queen Elizabeth's School
https://qes.pt/
Alvalade, Lisboa

My daughter went there after doing her first year infants in the UK (in our 'gap year' there)
She is still there and loves it to bits, doing really well
We love it too

Lessons in Portuguese in the morning, in then in English (with native speakers) in the pm plus others (e.g. primary science) so they have two class teachers.
Tennis and science and English clubs included in price
Looks old school UK, but has the warmness of the Portuguese
Huge majority are Portuguese kids, with a fair number of internationals
Reasonable fees (which also means that money isn't everything in the playground and at the school gates ...)

Creche 12 to 36 months
'Infantil' 3, 4 & 5 years
'Básico' up to year 4

Catholic but very moderate and teach excellent values (my only initial worry - completely OK)
Ex-pupils have a great reputation when they move on to big school
Everyone I have met who went there (some are now over 60) say they only have good memories 🙂