What to buy my nieces 4yrs, 2yrs, 1year, and nephew 3yrs old??! Help!

[SylvaniansKeepGettingHoovered]

So I need to get xmas presents for:

4yr old niece
2yr old niece
15 month old niece
3yr old nephew

Any suggestions anyone? In the past I've spent too much, around £25 each, but this year I need to cut down to around £15 on each of them. I have two daughters of my own to buy for! I was thinking of getting pyjamas/onsie for them, but I have a feeling someone else in the family is already doing that so I don't really want to duplicate.

Are they all one family? If the 4 yr old is anything like mine then anything frozen themed or barbie! Could you get some happy land for the 15 month and 2 year olds- there is bound to be a sale around half term. Or a tea set and some pretend food?
I'm not so hot on boys but depending on whether he is just 3 or nearly 4. If nearly 4 then Lego juniors might be appreciated.

4yr old id say anything Frozen related. Or one of those Galt craft tubs (£10 I think, we used ours loads)

2yo Djecco peg mosaic board (my dd enjoyed at 2 and adored at 3) and Jack and the Flum Flum Tree book (really fab)

15mo niece magnetic fishing game, and book. again I think Djecco do a nice one. What the ladybird heard is good for that age range book wise. aqua doodle also a good option for that age.

3yo nephew, remote control car??

I have a 4yr old DD and Niece.

Recently bought my niece on of these for her birthday which she loved. DD has one hidden for her stocking.
Little live birds

Plenty of Frozen themed gifts heading their way too!