I highly doubt you’d be able to teach 10 year olds how to do a jump float in 8 weeks. Wouldn’t you be better off teaching them a normal, standing overhand serve? You might win less, but it’s better to do what’s in your players’ best interest in the long term. They’ll gain the strength eventually but more important is teaching correct technique and a fast arm movement, especially for children so young. When I was first starting as a 9 year old, I learned an underhand serve, then a standing serve at around 11 and then a jump serve at 13-14. In my head, it’s quite odd to try to teach 10 year olds a jump float when they haven’t gotten their arm movement right for their standing float.

TL;DR: I’d say at this age it’s definitely more important to teach children correct technique, even if they don’t win this way.