This infuriates me. My son would move his focus to something else, and would subsequently be distracted by noises and flashing lights.

It reminds me of 'attract mode' used in slot machines and arcades games, though I at least see that there's direct commercial benefit to this.

Stealing my child's attention for no significant gain to them is plain wrong. Perhaps the commercial rationale is that the toy appears to be more popular than it really is, leading to further sales.

Or perhaps the developers just had a few hundred bytes and a timer interrupt to spare.

We nicknamed one of the toys are kids were given, "needy ball" because it did this. Fortunately, our kids generally prefer toys they could play with instead of toys that wanted to play with them.

Those are first on my list for disassembly per the sibling comment.