During these ages your baby will have a lot of both physical and cognitive growth and development.
Toys to assist with this time include;
Your baby will engage best with high contrast and bright colours.
Sensory toys including ones that stimulate sound and also tactile toys are best.
When your child begins to sit is both a huge physical and also cognitive milestone. During this time they will view the world from an entirely different angle which encourages use of different more vertical toys.
Once sitting it is time to move onto the next age group of 6-12 month toys.
*Main safety to consider is your child is likely to mouth objects. Make sure it is safe for them to do so.