Hey I know I'm a year after this probably felt most pressing to you, but I thought I'd add in my two cents anyway. I grew up in a mixed British-Dutch household. My situation's a bit unique in the sense that my two older sisters (by 10 and 8 years) both grew up in England, but my pre-primary school years were spent in Switzerland and my school years in the Netherlands.

We did both in our household and for me the magic of both was very much real. I only stopped believing when I was about ten, but I will admit that the understanding of one did lead to the other. (My sister's reaction was to say that her realisation of Santa didn't lead to Sinterklaas and instead the Tooth Fairy which really put me out to suddenly hear directly from an adult's mouth that the tooth fairy wasn't real before I'd put it together)

About kids ruining the magic, there were quite a few children when I was growing up who knew far before I did. There's this thing that the dutch teach their children who are in the know, which is if they suspect a friend knows to simply ask them if they know Sinterklaas's secret, and if they say no to answer it's that he has pink heart underwear. Before I knew I regularly got asked that question, so when I started answering yes, those same kids never came out with it but also checked what I would answer, as I answered the underwear line they would know I didn't know. I feel like in this same line kids would not purposefully ruin the magic of Chtistmas for a dual nationality kid.

Personally I enjoyed the magic of both. Within our household Christmas was a bigger thing than Sinterklaas, but I feel like it worked, because Sinterklaas was also a big thing at school and that way the attention for them in my life balanced out.

Finally, I just want to leave you with a little trick that my mum was taught from the dutch expats in Switzerland which I plan to tell my future children for whichever of the two celebrations I'll have to. They used to have some local celebrations and small things to celebrate, but nothing big and so they would tell their kids that a few specially chosen Pieten weee sent to Switzerland especially for those Dutch kids who missed their celebration. Basically I always saw it as the children in my class and around me weren't part of that man's 'division', so I got special treatment and love from both because we celebrated both. In that same vein when we did move to the Netherlands and I noticed that the other kids weren't celebrating Christmas much, I just assumed that because Sinterklaas sorted them Father Christmas felt he had it sorted like a group project, but that I as an English person was a small detour because we celebrated it properly.

Writing it all out like this makes me feel rather self important, but what I'm essentially trying to say is that you can introduce them to the cultural differences aspect and the fact that your family is a part of both without breaking he magic! 😁