in thinking an voucher would be ok for a gift

[countstropular]

for a 3 year old? (birthday)

Depends on who the three year old is really. Are they a relation or friend/distand friend?

YANBU

Its for a joint party where the child isnt the one ds knows as well. We have a gift for the "friend".

Oh in that case it sounds ideal.

Personally though I'd be more inclined to put money in the card because if a child gets vouchers for different shops, I always think it's a shame they cant club them together and get something they may really want...but I realise that's a personal choice.

I'm sure either will be much appreciated

Absolutely. At Xmas we got grandaughter a couple of cheap colouring books (so that she had something to open and play with on the day), and put ELC voucher in the card so that her mum could use it to get something that she hadnt already got, or to add to something she has. GD is 5 in March and we will do similar again.

As long as for a childs shop that they would recognise then its fine.