If I think 4 years seems a little optimistic as the starting age for a discovery made by myself, I still think good company, a child even younger, is likely to focus at least the aspects rhymes / sound effects / gaming . For larger manipulations are multiple: it really is a whole world of discovery that awaits them and that can be done solo even if playback is stuttering.
Very good point: the ability to modulate the sound of the pen, this lack of modulation is a very common fault on games (educational or not) for children, Ravensburger avoids the pitfall, adults will be grateful ^^
A small flat on the difficulty opening the battery compartment pen, really not easy, but it's a minor fault! Jémettrais also some reservations about the strength of books in the hands of a 4 year old child left unattended ...
The tiptoi really is an exciting educational game (the two things are not always compatible alas) that will not leave your child in circles or get bored after a few minutes. A particularly durable toy that extra pounds can further enlarge the discoveries and prospects even offer the option to toy with the child for several years.
A good toy that will make many happy little curious!