I think you have pretty much nailed it. I like your layout. I have heard of people burning themselves on a hot radiator as they reached for a towel or got out of the bath but that's a practical place for the rad. Windows are unobstructed, it's good. The orientation of the door is good too as it opens against the bath and not the basin. Practical if you just need to wash your hands quickly. I have some bathroom doors that open outward and inward. Not sure which is more preferable? Just consider if you bathing small children that the panel for the shower is not too rigid as it's harder to use the bath. A pivot type is better for cleaning too.

Your layout seems very well thought out. Here are a few practical things to consider. Choose a bath with a non slip base safe for standing when showering but is also comfortable to lie on. Install a dual shower head system with a longer than average hose which makes children’s hair washing easier and helpful when cleaning the bath. As Isla says, a pivot screen is essential to make it easier to bathe children but also to reach the bath taps. A bath with wide ledges which can hold containers for toiletries, sponges, toys and so on is also handy. As is a sink unit wide enough for hand-soap, toothbrush holders, etc. Having a large sliding door mirrored wall unit above the sink (not the toilet!) is also great for keeping your surfaces clear. I would always choose wall panels instead of tiles as they’re much easier to keep clean.

And a ladder style towel radiator big enough to accommodate wet towels is a must.

If you go for large format porcelain tiles with minimal grout you will never have a cleaning problem either. I have 600mm sq porcelain tiles (Lusso Stone) with 2mm epoxy grout. Happy days :) Betty Boo is 100% right. Get a hand shower attachment. So much easier for little ones. Also useful for just washing your hair over the bath.

How about storage? Toilet rolls, toiletries etc. There never seems to be enough in today’s bathrooms.

Depending on the hardness of your water I would choose the best quality shower fittings and tap as possible. Also choose a front mounted shower with a riser rail and a hand shower attachment. Much easier for maintenance. Grohe, Hansgrohe or Vado are all good makes. The cheaper taps usually fail/leak within a short time and the cartridge is almost as expensive as replacing the whole tap. Like with printer ink.