android apps foundation/ks1/ks2 - free or cheap?

[3birthdaybunnies]

Have just got a new phone and the dc are keen for me to get some apps on mine, like daddy's. I'm wanting some more educational ones, his phone has the angry birds type games on, I can see that there is a tiny bit of geometry, but really wanting some which will specifically support their learning so they won't bug me to use my phone and use dh's instead .

Should say, youngest is 3; can count, recognise numbers but still learning letters, the other two are nearly 6 and 8 respectively and kind of top end of average ability for their year groups.