You wanted the side menu and the drawing rail to carry the child's chosen colour, a grown-ups button that does not look tacked on, and the home button and page name to feel like they belong. Here are three takes on the whole navigation system. Same app, three personalities. Pick one and I build it into both prototypes.
Marko no longer peeks over the canvas on the drawing page. The art is the only thing down there now.
Sidebar and the left tool rail both carry the child's colour, so the app feels like theirs.
No more three floating islands up top. The back control and the page name are grouped so they read as "where am I".
Grown-ups can turn the "ask a grown-up" step off for the camera. Shown at the bottom.
The menu is a rounded dock of the child's colour that floats off the edge, like a friendly object sitting on the desk rather than a wall of paint. Nav are frosted white circles; the grown-ups door is set apart below a divider so a kid reads it as the way out, not another toy.
The dock floats, so full-saturation blue never feels like a heavy slab. The grown-ups control is a quiet frosted lock, physically separated by a hairline and a gap, so it never competes with the three big nav circles a child actually uses. On the drawing screen the back arrow and the page name live in one connected pill ("back from T-Rex"), and the tool rail is the exact same dock material as home, so the two screens feel like one app.
A confident full-height panel in the child's colour, flush to the edge with a soft top-to-bottom gradient. iPad has the room, so nav items get words as well as icons. The grown-ups door is pinned to the very bottom as a dark footer bar, unmistakably a utility and not a peer of the nav.
This is the most structured, most "designed" read. Labels under the icons help early readers and parents. The active item is a clean white card, so the current screen is never in doubt. The grown-ups footer bar is the strongest separation of the three: it looks like a settings drawer handle, not a fourth activity. On the drawing screen the page name sits as real bold text beside the back arrow, not a floating pill, which is what fixes the "out of place" feeling.
The most refined take. The rail is a whisper of the child's colour over cream, and the blue turns up to full strength inside the controls: the active tab is a solid blue circle with a soft glow. Loud where it matters, calm everywhere else. The grown-ups exit is a deliberately small, quiet control so little hands do not gravitate to it.
If full blue ever starts to feel loud next to the artwork, this is the answer: the colour is unmistakably the child's, but it rides the buttons and the active glow instead of a solid slab, so the line art stays the hero. The drawing screen uses a proper slim top toolbar that spans the width and holds the back arrow, the page name and Save in one clean strip, the most conventional and self-explanatory of the three.
New toggles let a parent drop the "with a grown-up" tag and skip the maths gate before the camera, for families who would rather it just open.
One flag from me: to keep the 4+ App Store rating, the gate legally needs to stay on by default, because a photo leaves the device for the AI. I would ship it ON, clearly labelled, so turning it off is the parent's informed choice. Easy to build either way.