I spoke to a cake baker (Cheryl The Baker.. you can find her on facebook/instagram and see the pictures of her cakes too) about this before. Sugar is needed for moisture to get the cake texture, otherwise you get a biscuit 😂 Some bakers can use less sugar or an alternative sweetener (eg. iLite, but this ingredient is 10x as expensive as sugar). Chia seeds/flax seeds/dates may be used, so if you want to hide these ingredients in the appearance of the cake, you’ll need like chocolate flavour. Otherwise, in a light coloured cake, you’ll see all these seeds, which may not look so nice. Cheryl The Baker has done a reduced sugar cake for me. She said other places with baby friendly cakes include Delcies and Locaba. Hope you manage to get what you want:)
If you don't mind baking yourself there are lots of recipes online that don't have sugar & eggs. I made one for my baby's birthday and she really enjoyed it :D.
sugarmill, delcies :)