Totally up to you, but a kids room should be fun and whimsical especially if this isn't the bathroom that guests are using. Have some fun with it, maybe even let the kids choose from your shortlist of tiles that you like so they feel like they had some say in their own bathroom. =)

ask yourself who you are you aiming to please..is the house for your own family or for immediate resale although i'd be reluctant to make the family bathroom too small child focussed as small children become sophisticated teenagers very quickly and personal decorative elements can be added with colourful towels and a collection of bath toys

How old are your kids?
I would not let my 5 year old choose the decor. The bathroom is a expensive room to refit if down the track your, now 15 year old, is bathing in a wiggles coloured bathroom.
I think homes should flow, with all rooms a similar colour palette. Accents of colour by accessories are a lot easier to change.

I like some tie in whether it be vanity style, tile type, taps, but def can have own personality as long as en-suite stars

There is absolutely no rules. But given most people struggle to makedecisions on bathroom fittings in not sure why you would put yourself through the pain of having to double the selection options!
I would suggest putting a moodboard together of all the finishes you like and then work out how to divide between two rooms. E.g. maybe keeping floor tiles the same but having different feature tiles (if that's your cup of tea) in each room.

Hi Rebecca, I think that is a good idea. And in five years time, there will be an adult using the kids bathroom also.