1 cup flour
1 cup warm water
2 teaspoons cream of tartar
1 teaspoon oil
1/4 cup salt
Mix all ingredients, adding food coloring last. Stir over medium heat until smooth. Remove from pan and knead until blended smooth. Place in plastic bag or airtight container when cooled. Will last for a long time. Source
For other variations, you can check other fun play dough recipes. But if you really don't want to bother, you can just buy from Ilog Maria or department/toy stores (Play Doh).
Now, Play-Doh seems to have a monopoly of the commercially distributed clay. They're selling four tubs for P130 which isn't bad since their clay has been tried and tested to last and not irritate.
But what do you do if you want more clay molds but don't want to pay a higher price for it? For that, you can go to Divisoria. Anding's Toy Store has several box sets of molds that you can buy (there's even a farm set with a Play-Doh-like fun factory squeezer). They'd cost between P130-150 per set and each set contains clay also. Of course, if your child is still prone to tasting things or if your child has sensitive skin, i'd suggest not to use the clay that comes with these molds anymore. Maybe you (the adult) can use them instead.
sample of molds you can get at Divi
You can also freely use your kid's other toys. Toy pans and pots sometimes have bottoms that can create texture on clay. Other fun shapes from other toys can be used as molds also.
And what do you do when the clay has hardened? Just add some water and knead the dough, and keep adding some water until you get the desired consistency. Also make sure that the clay dough is stored in airtight containers. If you're not using them for a while, store the dough in the airtight containers with some water, which the clay will absorb while it's stored.
Playing with clay is really relaxing and helps your little ones with hand dexterity and creativity. Just make sure they don't ingest anything (even if homemade play doughs are non-toxic) and don't play with small parts that could pose a choking hazard.