My top pics for maths , in order of preference, are:
Curriculum - We are using Singapore Maths, which I love. I tried Saxon K but I didn't like it.
DVDs - Mathtacular DVDs are great. I set my 4 year old up at her table with her maths manipulative and let her work along with the DVD
Living Math books - this is probably my favourite option for ease of use. Check out Math Start books, Sir Cumference etc. If you search for these on Amazon, you will find lots of other suggestions.
Cuisinaire rods - check out the free videos on
www.educationunboxed.com for ideas on how to use them. I just got them and my 4 year old loves them. They can be used from approx age 2 early number sense right up through multiplication, division and fractions.
Music - I use Peter Weatherall maths music cds in the car.
Apps - Euro Talk Maths
Books - check out Kitchen Table Maths - I found this better than Marshmallow Math.
All of these would be suitable for both of your kids. Good luck!