There's a soft play centre in Amlwch called Sbri Môn, and one in Bodffordd , LLangefni if you need somewhere dry to play. Pili Palas is a butterfly house on the island, and should you have nice days, there are two farms you could visit : Foel farm with plenty to see and do and has a chocolate factory on site. Henblas is the other with animals, tractor rides and duck displays - they also have an indoor play area with a big bounce castle ( maybe for older children?) PLenty of walks - Dingle in Llangefni is pushchair friendly with a wooden pathway through the trees. Holyhead has two lovely coastal parks - Penrhos and Breakwater park (which runs a land train on weekends.) There's also a small cinema in Holyhead (one screen) called the Empire. I feel like the Anglesey tourist board! Have fun x
Henblas is FAB FAB FAB!! I used to go when i was younger and we took DS1 a few years ago and he loved it too.
Pili Palas i know i have been to and enjoyed but there are some MASSIVE butterflies which still guive me the heeby jeebies!!
There used to be an enormous post office in Valley on the left just before you get to the train station (if you are going towards Amlwch) that sold EVERYTHING, am sure there would be something to find in there if it's still there.
Traddur Bay beach is nice in drizzle with waterproofs and wellies on and i think that the lifeboat house has a bit in to look around but my knowledge of that beach is mostly from before there was even alifeboat house!